playsink: Only remove the complete text chain if the text pad goes away
If the text pads does not go away we just set the overlay to silent, which allows us to immediately re-enable subs later again. However before this change we also released the streamsynchronizer text pads, which deadlocked because there was still dataflow going on. Just do this only if we remove the complete chain. https://bugzilla.gnome.org/show_bug.cgi?id=683504