OBB: track binder death observers

An incorrect assumption about how death observers were tracked lead to
an IllegalArgumentException in some cases. Make sure the linking and
unlinking of the Binder to its ObbState death observer is symmetric to
avoid this problem.

Bug: 3062360
Change-Id: Idd016db12551c80cd74d00f11cf6569bd3b4ce21
1 file changed