st: Remove StIconType

GTK+ works by explicitly specifying a -symbolic suffix for all icons.
Do the same here.

https://bugzilla.gnome.org/show_bug.cgi?id=682540

js/ui/panelMenu.js

@@ -242,7 +242,6 @@ const SystemStatusButton = new Lang.Class({
 
     addIcon: function(gicon) {
         let icon = new St.Icon({ gicon: gicon,
-                                 icon_type: St.IconType.SYMBOLIC,
                                  style_class: 'system-status-icon' });
         this._box.add_actor(icon);