timed-revealer: Fix "revealer" refcounting
virt_viewer_timed_revealer_new calls gtk_container_add on the instance
returned by gtk_revealer_new so VirtViewerTimedRevealer does not own any
ref on this GtkRevealer instance. Unrefing it in _dispose() is thus wrong.
Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>
Acked-by: Fabiano FidĂȘncio <fidencio@redhat.com>