Audio service: always unduck focus winner

When a FocusRequester gains focus, always unduck it.
This fixes a bug where a player could remain ducked even after
  regaining focus. The issue was that the unducking was only
  done in the focus gain if the loss had been
  AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK, which is the only one
  that could have caused a duck. But between the moment
  the app lost audio focus with LOSS_TRANSIENT_CAN_DUCK and
  the moment it regains focus, it could have lost the focus
  once more with LOSS_TRANSIENT. And in this case, it would
  not have been unducked.
The fix consists in always unducking an app that gains focus. If
  it wasn't ducked, that operation is a no-op.

Test: see bug
Bug: 37433811
Change-Id: I95a5bfcc2d5063986bd62841c1893bbbd00b45bf