gtk: remove "gboolean homogeneous" from gtk_box_new()

Because it's FALSE in virtually all use cases.

demos/gtk-demo/main.c

@@ -954,7 +954,7 @@ main (int argc, char **argv)
   g_signal_connect_after (window, "destroy",
 		    G_CALLBACK (gtk_main_quit), NULL);
 
-  hbox = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, FALSE, 0);
+  hbox = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 0);
   gtk_container_add (GTK_CONTAINER (window), hbox);
 
   tree = create_tree ();