window: Remove needless call to ensure_state_flag_backdrop() on map

This call was forcing needless work since gtk_window_map() already
does a gdk_window_show() which initially sets GDK_WINDOW_STATE_FOCUSED
that we then handle regularly on the widget's window state event
handler.

https://bugzilla.gnome.org/show_bug.cgi?id=673237

gtk/gtkwindow.c

@@ -5008,8 +5008,6 @@ gtk_window_map (GtkWidget *widget)
     gtk_window_set_focus_visible (window, gtk_window_get_focus_visible (priv->transient_parent));
   else
     gtk_window_set_focus_visible (window, visible_focus == GTK_POLICY_ALWAYS);
-
-  ensure_state_flag_backdrop (widget);
 }
 
 static gboolean