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/notificationDaemon.js

@@ -357,7 +357,6 @@ const NotificationDaemon = new Lang.Class({
 
         let gicon = this._iconForNotificationData(icon, hints);
         let iconActor = new St.Icon({ gicon: gicon,
-                                      icon_type: St.IconType.FULLCOLOR,
                                       icon_size: MessageTray.NOTIFICATION_ICON_SIZE });
 
         if (notification == null) {