main: make "gnome-shell" the default gettext domain

Since libmutter uses dgettext(), we can take over the default domain

https://bugzilla.gnome.org/show_bug.cgi?id=649203

js/ui/environment.js

@@ -7,7 +7,7 @@ imports.gi.versions.GdkPixbuf = '2.0';
 imports.gi.versions.Gtk = '3.0';
 
 const Clutter = imports.gi.Clutter;;
-const Gettext = imports.gettext.domain('gnome-shell');
+const Gettext = imports.gettext;
 const GLib = imports.gi.GLib;
 const Gtk = imports.gi.Gtk;
 const Shell = imports.gi.Shell;