xwayland: Don't take buffer release queue into account for frame timer

The buffer release queue has two kinds of entries:

* Pending async flips.
* Completed flips waiting for their buffer to be released by the Wayland
  compositor.

xwl_present_timer_callback neither completes async flips nor releases
buffers, so the timer isn't needed for the buffer release queue.

(cherry picked from commit e6cd1c9bdefe83e7d99b703a68d26eebb451f889)

hw/xwayland/xwayland-present.c

@@ -86,8 +86,7 @@ static inline Bool
 xwl_present_has_events(struct xwl_present_window *xwl_present_window)
 {
     return !!xwl_present_window->sync_flip ||
-           !xorg_list_is_empty(&xwl_present_window->event_list) ||
-           !xorg_list_is_empty(&xwl_present_window->release_queue);
+           !xorg_list_is_empty(&xwl_present_window->event_list);
 }
 
 static void