wayland: Replace buffer destroy wl_signal with a GObject signal

Don't use the libwayland-* utilities when we have our own that do the
same thing.

https://bugzilla.gnome.org/show_bug.cgi?id=762828

src/wayland/meta-wayland-surface.h

@@ -104,7 +104,7 @@ struct _MetaWaylandPendingState
   /* wl_surface.attach */
   gboolean newly_attached;
   MetaWaylandBuffer *buffer;
-  struct wl_listener buffer_destroy_listener;
+  gulong buffer_destroy_handler_id;
   int32_t dx;
   int32_t dy;