Remove session from user engaged list when destroyed

This prevents references to a destroyed session being kept forever
Also more clearly clean out the final state in MediaSessionRecord

Test: Verified references are gone in heapdump
Flag: com.android.media.flags.enable_notifying_activity_manager_with_media_session_status_change
Bug: 295518668
Change-Id: If5b50c8ffc9be0078a12ca1bccf17e7b30bbd8e3