libweston: Notify timeline of object modification

We notify the timeline of the fact that the object suffered
modifications through the 'set_label' function. Remove the old
refresh variable.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
diff --git a/libweston/compositor.c b/libweston/compositor.c
index 420bc84..26a62c7 100644
--- a/libweston/compositor.c
+++ b/libweston/compositor.c
@@ -4088,7 +4088,8 @@
 					  char *, size_t))
 {
 	surface->get_label = desc;
-	surface->timeline.force_refresh = 1;
+	weston_timeline_refresh_subscription_objects(surface->compositor,
+						     surface);
 }
 
 /** Get the size of surface contents