Don't mention gtk_set_locale() in docs; this function does not exist

gtk/gtkmain.c

@@ -59,8 +59,8 @@
  * int
  * main (int argc, char **argv)
  * {
- *   /* Initialize i18n support */
- *   gtk_set_locale ();
+ *   /* Initialize i18n support with bindtextdomain(), etc. */
+ *   ...
  *
  *   /* Initialize the widget set */
  *   gtk_init (&argc, &argv);