Remove simple uses of ClutterRectangle

https://bugzilla.gnome.org/show_bug.cgi?id=699975

js/ui/dnd.js

@@ -43,7 +43,7 @@ let dragMonitors = [];
 
 function _getEventHandlerActor() {
     if (!eventHandlerActor) {
-        eventHandlerActor = new Clutter.Rectangle({ width: 0, height: 0 });
+        eventHandlerActor = new Clutter.Actor({ width: 0, height: 0 });
         Main.uiGroup.add_actor(eventHandlerActor);
         // We connect to 'event' rather than 'captured-event' because the capturing phase doesn't happen
         // when you've grabbed the pointer.