The AudioFocus death handler was correctly updating the audio
focus stack when an audio focus client dies, but the death handler
was leaking GREF if unlinkToDeath() is not called.
The fix consists in making sure unlinkToDeath() is always called
by calling it in its finalizer.
Change-Id: I0c5343b4986ab582cadbf171fc53816952dc16f5
de1f065be1