This leaves only the existence of audioserver domain as public API.
All other rules are implementation details of this domain's policy
and are thus now private.

Test: No change to policy according to sesearch, except for
      disappearance of all allow rules to do with audioserver_current
      except those created by other domains' allow rules referencing
      audioserver domain from public and vendor policies.
Bug: 31364497

Change-Id: I6662394d8318781de6e3b0c125435b66581363af