appDisplay: Add missing .actor

This was missed while cherry picking
b88f7d0655 to 3.34.

Thanks to Térence Clastres for finding the issue and testing.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/852

js/ui/appDisplay.js

@@ -179,7 +179,7 @@ class BaseAppView {
             let id = icon.id;
 
             this._allItems.splice(iconIndex, 1);
-            icon.destroy();
+            icon.actor.destroy();
             delete this._items[id];
         });