Bug 1606554 - Remove accidently introduced stub gdk_window_get_visible_region. r=ntim

Differential Revision: https://phabricator.services.mozilla.com/D69508

--HG--
extra : moz-landing-system : lando

widget/gtk/mozgtk/mozgtk.c

@@ -509,7 +509,6 @@ STUB(gtk_window_get_modal)
 STUB(gtk_window_get_transient_for)
 STUB(gtk_window_get_type)
 STUB(gtk_window_get_type_hint)
-STUB(gdk_window_get_visible_region)
 STUB(gtk_window_get_window_type)
 STUB(gtk_window_group_add_window)
 STUB(gtk_window_group_get_current_grab)