st: Remove custom text direction stuff

Clutter has its own built-in system for managing text directions, like GTK+.
Convert over to use this.

https://bugzilla.gnome.org/show_bug.cgi?id=670034

js/ui/dateMenu.js

@@ -52,7 +52,7 @@ const DateMenuButton = new Lang.Class({
         let vbox;
 
         let menuAlignment = 0.25;
-        if (St.Widget.get_default_direction() == St.TextDirection.RTL)
+        if (Clutter.get_default_text_direction() == Clutter.TextDirection.RTL)
             menuAlignment = 1.0 - menuAlignment;
         this.parent(menuAlignment);