popupMenu: Ungrab when removing active menu

While we do have some handling for removing the active menu, it has
been a no-op for years. The bit that we really care about from the
PopupMenuManager's point of view is the existing grab though. Drop
that instead of calling _closeMenu() directly; ungrabbing will still
call the method indirectly, and it will still be a no-op :-)

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/3022

js/ui/popupMenu.js

@@ -1325,7 +1325,7 @@ var PopupMenuManager = class {
 
     removeMenu(menu) {
         if (menu == this.activeMenu)
-            this._closeMenu(false, menu);
+            this._grabHelper.ungrab({ actor: menu.actor });
 
         let position = this._findMenu(menu);
         if (position == -1) // not a menu we manage