xdg-shell: Remove the flags from get_xdg_popup

There haven't been any ideas for flags, so we don't need a useless,
unused parameter hanging around. Any future ideas should be done with a
new request entirely.

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

clients/window.c

@@ -4840,8 +4840,7 @@ window_show_menu(struct display *display,
 						    input->seat,
 						    display_get_serial(window->display),
 						    window->x - ix,
-						    window->y - iy,
-						    0);
+						    window->y - iy);
 	fail_on_null(window->xdg_popup);
 
 	xdg_popup_set_user_data(window->xdg_popup, window);