appDisplay: Drop grabHelper.addActor() call

This no longer does what it advertises to do, the folder dialog
is already modal and handles clicks outside to dismiss the dialog,
so this does not seem necessary either.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2046>

js/ui/appDisplay.js

@@ -2573,7 +2573,6 @@ var AppFolderDialog = GObject.registerClass({
         this._grabHelper = new GrabHelper.GrabHelper(this, {
             actionMode: Shell.ActionMode.POPUP,
         });
-        this._grabHelper.addActor(Main.layoutManager.overviewGroup);
         this.connect('destroy', this._onDestroy.bind(this));
 
         this._dragMonitor = null;