Customizer: Remove a `throw error` call which prevents further actions, like `jqxhr.always()`.

props westonruter.
fixes #31501.

git-svn-id: https://develop.svn.wordpress.org/trunk@31816 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/js/customize-widgets.js

@@ -1852,12 +1852,7 @@
 			controlContainer.slideDown( function() {
 				if ( isExistingWidget ) {
 					widgetFormControl.updateWidget( {
-						instance: widgetFormControl.setting(),
-						complete: function( error ) {
-							if ( error ) {
-								throw error;
-							}
-						}
+						instance: widgetFormControl.setting()
 					} );
 				}
 			} );