Audio focus doesn't affect RemoteController

The top of the stack of PlayerRecord instances is the "promoted"
 instance whose RemoteControlClient information is available
 to RemoteController objects, only when it also has audio focus.

This change removes the condition on audio focus ownership:
- whenever the player record stack ordering changes, no need to
  check if it also has audio focus
- since the player record and audio focus stacks operate separately,
  there is no need to synchronize access to both stacks.

Change-Id: I668f2aa2950f19f8c2a30bc59c7352246edcc56e