Remove unneeded color-setting code in the boards and library manager

Previously, for the boards manager:
 - InstallerJDialog would set the "selection background" color on the
   table, using the "status.notice.bgcolor" the color (default blueish
   green). This color is not used directly, but made available for cell
   renderers to use.
   a1448876a1/app/src/cc/arduino/contributions/ui/InstallerJDialog.java (L183)
 - For each cell, either a ContributedPlatformTableCellEditor or
   ContributedPlatformTableCellRenderer is used, depending on whether
   the cell is being edited (i.e. when selected).
 - Both of these create a ContributedPlatformTableCellJPanel, and call
   its `update` method, which creates the components for the cell.
 - The `update` method als sets the background color of the description
   to white, which does not actually have any effect because the
   description is not opaque.
   a1448876a1/app/src/cc/arduino/contributions/packages/ui/ContributedPlatformTableCellJPanel.java (L271)
   a1448876a1/app/src/cc/arduino/contributions/packages/ui/ContributedPlatformTableCellJPanel.java (L309)
   https://docs.oracle.com/javase/7/docs/api/javax/swing/JComponent.html#setBackground(java.awt.Color)
 - The `update` method also sets its colors of itself (JPanel) to the FG
   and BG color, or the selected FG and BG color of the table depending
   on the selected status of the cell. These seem to default to black on
   white for non-selected and white on blue-ish for selected cells.
   However, InstallJDialog has replaced the selected BG with a blueish
   green, as shown above.
   Of these, only the BG colors actually seem to take effect. The fg
   color of the description component is actually used (default black).
   a1448876a1/app/src/cc/arduino/contributions/packages/ui/ContributedPlatformTableCellJPanel.java (L282-L288)
 - After calling `update`, ContributedPlatformTableCellEditor overrides
   the JPanel background color with a fixed grey color. Similarly,
   ContributedPlatformTableCellRenderer sets an alternating white and
   (slightly lighter) grey background color. Together, this means that
   the background color set by ContributedPlatformTableCellJPanel is
   never actually used.
   a1448876a1/app/src/cc/arduino/contributions/packages/ui/ContributedPlatformTableCellEditor.java (L132-L133)
   a1448876a1/app/src/cc/arduino/contributions/packages/ui/ContributedPlatformTableCellRenderer.java (L47-L53)

For the library manager, pretty much the same happens.

Effectively, the only colors that were actually used were the background
colors set by ContributedPlatformTableCellEditor and
ContributedPlatformTableCellRenderer. This is problematic because:
 - There is a lot of other confusing and unused code
 - The foreground color is never set. This is fine when it is black or
   another dark color, but when the system is configured with a dark
   theme, the default foreground color will be white, which is
   problematic on a white background.

This commit remove the unneeded code, setting the foreground color
is left for later. It also removes the (now unused) `isSelected` from
`ContributedPlatformTableCellJPanel::update`. For the library manager,
the corresponding argument is still used to decide the "author" color.

app/src/cc/arduino/contributions/libraries/ui/ContributedLibraryTableCellJPanel.java

@@ -199,7 +199,6 @@ public class ContributedLibraryTableCellJPanel extends JPanel {
     description.setText(desc);
     // copy description to accessibility context for screen readers to use
     description.getAccessibleContext().setAccessibleDescription(desc);
-    description.setBackground(Color.WHITE);
 
     // for modelToView to work, the text area has to be sized. It doesn't
     // matter if it's visible or not.
@@ -209,14 +208,6 @@ public class ContributedLibraryTableCellJPanel extends JPanel {
     InstallerTableCell
         .setJTextPaneDimensionToFitContainedText(description,
                                                  parentTable.getBounds().width);
-
-    if (isSelected) {
-      setBackground(parentTable.getSelectionBackground());
-      setForeground(parentTable.getSelectionForeground());
-    } else {
-      setBackground(parentTable.getBackground());
-      setForeground(parentTable.getForeground());
-    }
   }
 
   // same function as in ContributedPlatformTableCellJPanel - is there a utils file this can move to?

app/src/cc/arduino/contributions/packages/ui/ContributedPlatformTableCellEditor.java

@@ -129,7 +129,7 @@ public class ContributedPlatformTableCellEditor extends InstallerTableCell {
     cell.versionToInstallChooser
         .setVisible(installed == null && uninstalledReleases.size() > 1);
 
-    cell.update(table, _value, true, !installedBuiltIn.isEmpty());
+    cell.update(table, _value, !installedBuiltIn.isEmpty());
     cell.setBackground(new Color(218, 227, 227)); // #dae3e3
     return cell;
   }

app/src/cc/arduino/contributions/packages/ui/ContributedPlatformTableCellJPanel.java

@@ -175,8 +175,7 @@ public class ContributedPlatformTableCellJPanel extends JPanel {
     return retString;
   }
 
-  void update(JTable parentTable, Object value, boolean isSelected,
-              boolean hasBuiltInRelease) {
+  void update(JTable parentTable, Object value, boolean hasBuiltInRelease) {
     ContributedPlatformReleases releases = (ContributedPlatformReleases) value;
 
     JTextPane description = makeNewDescription();
@@ -262,7 +261,6 @@ public class ContributedPlatformTableCellJPanel extends JPanel {
     description.setText(desc);
     // copy description to accessibility context for screen readers to use
     description.getAccessibleContext().setAccessibleDescription(desc);
-    description.setBackground(Color.WHITE);
 
     // for modelToView to work, the text area has to be sized. It doesn't
     // matter if it's visible or not.
@@ -272,14 +270,6 @@ public class ContributedPlatformTableCellJPanel extends JPanel {
     int width = parentTable.getBounds().width;
     InstallerTableCell.setJTextPaneDimensionToFitContainedText(description,
                                                                width);
-
-    if (isSelected) {
-      setBackground(parentTable.getSelectionBackground());
-      setForeground(parentTable.getSelectionForeground());
-    } else {
-      setBackground(parentTable.getBackground());
-      setForeground(parentTable.getForeground());
-    }
   }
 
   private JTextPane makeNewDescription() {

app/src/cc/arduino/contributions/packages/ui/ContributedPlatformTableCellRenderer.java

@@ -44,7 +44,7 @@ public class ContributedPlatformTableCellRenderer implements TableCellRenderer {
                                                  int column) {
     ContributedPlatformTableCellJPanel cell = new ContributedPlatformTableCellJPanel();
     cell.setButtonsVisible(false);
-    cell.update(table, value, isSelected, false);
+    cell.update(table, value, false);
 
     if (row % 2 == 0) {
       cell.setBackground(new Color(236, 241, 241)); // #ecf1f1

app/src/cc/arduino/contributions/ui/InstallerJDialog.java

@@ -180,7 +180,6 @@ public abstract class InstallerJDialog<T> extends JDialog {
     contribTable.setDragEnabled(false);
     contribTable.setIntercellSpacing(new Dimension(0, 1));
     contribTable.setShowVerticalLines(false);
-    contribTable.setSelectionBackground(Theme.getColor("status.notice.bgcolor"));
     contribTable.addKeyListener(new AbstractKeyListener() {
 
       @Override