Remove a stray bit of user data

We don't need to pass a user_data argument to Meta.later_add() any
more, so remove a stray 'null'.

https://bugzilla.gnome.org/show_bug.cgi?id=615590

js/ui/main.js

@@ -485,7 +485,7 @@ function _queueBeforeRedraw(workId) {
         Meta.later_add(Meta.LaterType.BEFORE_REDRAW, function () {
             _runBeforeRedrawQueue();
             return false;
-        }, null);
+        });
     }
 }