window-list: Don't use 'panel-menu' class in bottom panel

Menus in the top bar have some margin at the bottom, to prevent
menus to extend all the way to the bottom edge as the expand; we
obviously don't want the same behavior in the window-list at the
bottom, so stop pretending to be a top bar menu.

https://bugzilla.gnome.org/show_bug.cgi?id=745952

extensions/window-list/extension.js

@@ -649,6 +649,7 @@ const WorkspaceIndicator = new Lang.Class({
     _init: function(){
         this.parent(0.0, _("Workspace Indicator"));
         this.actor.add_style_class_name('window-list-workspace-indicator');
+        this.menu.actor.remove_style_class_name('panel-menu');
 
         let container = new St.Widget({ layout_manager: new Clutter.BinLayout(),
                                         x_expand: true, y_expand: true });