popupMenu: Use TOPBAR_POPUP action mode for all menus

When it comes to keybindings or gestures, there's not really a good
reason why popups associated with the top bar should behave differently
from any other shell menus. Just set the action mode generically for
all menus, so actions like screenshots or media-keys start working
with menus like the background- or app launcher context menus.

https://bugzilla.gnome.org/show_bug.cgi?id=745039

js/ui/panel.js

@@ -723,7 +723,7 @@ const Panel = new Lang.Class({
 
         this.statusArea = {};
 
-        this.menuManager = new PopupMenu.PopupMenuManager(this, { actionMode: Shell.ActionMode.TOPBAR_POPUP });
+        this.menuManager = new PopupMenu.PopupMenuManager(this);
 
         this._leftBox = new St.BoxLayout({ name: 'panelLeft' });
         this.actor.add_actor(this._leftBox);