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/keyboard.js

@@ -542,7 +542,7 @@ const KeyboardSource = new Lang.Class({
 
     _init: function(keyboard) {
         this._keyboard = keyboard;
-        this.parent(_("Keyboard"), 'input-keyboard', St.IconType.SYMBOLIC);
+        this.parent(_("Keyboard"), 'input-keyboard-symbolic');
     },
 
     handleSummaryClick: function() {