audio: Fix for IPlayerShell object leak.

IPlayerShell object is created for each MediaPlayer object and
this will register to linkToDeath, which will have global
reference. IPlayerShell release method is unregistering to Death
monitor. Here IPlayerShell object is not released at all, when
application releases mediaplayer object. As linkToDeath will have
global reference for each IPlayerShell object, GC will not be able
to clear this object.

Fix is to call IPlayerShell release when application releases
mediaplayer object.

authored-by: Divya Narayanan Poojary <dnaray@codeaurora.org>
Test: manual
Bug: 65374542

Change-Id: Icbd7632d462d44efdbb851c1c8a662bdef0e551c