util: fix warnings when compiling gnome-shell-wayland

Replace our version of the gettext macros with those in glib,
so that they don't conflict with gnome-shell.

https://bugzilla.gnome.org/show_bug.cgi?id=707851

src/meta/util.h

@@ -25,6 +25,7 @@
 
 #include <glib.h>
 #include <glib-object.h>
+#include <glib/gi18n.h>
 
 #include <meta/common.h>
 
@@ -120,10 +121,6 @@ const char* meta_gravity_to_string (int gravity);
 
 char* meta_external_binding_name_for_action (guint keybinding_action);
 
-#include <libintl.h>
-#define _(x) dgettext (GETTEXT_PACKAGE, x)
-#define N_(x) x
-
 char* meta_g_utf8_strndup (const gchar *src, gsize n);
 
 void  meta_free_gslist_and_elements (GSList *list_to_deep_free);