Remove unneeded flexbug workaround (#40876)

This was only needed for Internet Explorer. Removing it saves a couple of bytes. :-)

REF: https://github.com/philipwalton/flexbugs#flexbug-4

scss/_card.scss

@@ -193,8 +193,7 @@
     // The child selector allows nested `.card` within `.card-group`
     // to display properly.
     > .card {
-      // Flexbugs #4: https://github.com/philipwalton/flexbugs#flexbug-4
-      flex: 1 0 0%;
+      flex: 1 0 0;
       margin-bottom: 0;
 
       + .card {

scss/mixins/_grid.scss

@@ -72,7 +72,7 @@
     @include media-breakpoint-up($breakpoint, $breakpoints) {
       // Provide basic `.col-{bp}` classes for equal-width flexbox columns
       .col#{$infix} {
-        flex: 1 0 0%; // Flexbugs #4: https://github.com/philipwalton/flexbugs#flexbug-4
+        flex: 1 0 0;
       }
 
       .row-cols#{$infix}-auto > * {