Fix circular structure typeerror in chromium

The variable ```params``` contains the member ```obj``` which does not seem to be of interest by the server. In chromium, this obj - member leads to an ```Uncaught TypeError: Converting circular structure to JSON``` when calling ```JSON.stringify``` on this ```params``` object in the ```storage.patchContact(...)``` function.

js/contacts.js

@@ -330,6 +330,7 @@ OC.Contacts = OC.Contacts || {};
 
 	Contact.prototype.deleteProperty = function(params) {
 		var obj = params.obj;
+		params = {};
 		if(!this.enabled) {
 			return;
 		}