AudioService: remove deprecated forcing of A2DP off

Forcing the policy to not use A2DP is not needed anymore now that
the cast icon does not expose A2DP choice anymore.
The corresponding AudioManager APIs have also been long deprecated.

Removing support for this feature which is replaced by newer routing
APIs.

Change-Id: If98572742a8cf6388c1408d015c86dd445c5660b