PlayerBase: unregistration in player release

The player state of PlayerBase was not kept in sync with its
  corresponding AudioPlaybackConfiguration. This caused
  the configuration to never be removed and gc'd because
  the state of PlayerBase when released was always the
  unitialized state of 0 == released state.

Test: use a MediaPlayer then call release, verify the player
  is not showing in the AudioService dumpsys
Bug: 30258418

Change-Id: I9a6704147949e1e45752e646648c8c882376752f