gtk: remove "gboolean homogeneous" from gtk_box_new()

Because it's FALSE in virtually all use cases.

tests/testinput.c

@@ -303,7 +303,7 @@ main (int argc, char *argv[])
   window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
   gtk_widget_set_name (window, "Test Input");
 
-  vbox = gtk_box_new (GTK_ORIENTATION_VERTICAL, FALSE, 0);
+  vbox = gtk_box_new (GTK_ORIENTATION_VERTICAL, 0);
   gtk_container_add (GTK_CONTAINER (window), vbox);
   gtk_widget_show (vbox);