This leaves only the existence of surfaceflinger 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
      surfaceflinger_current except those created by other domains'
      allow rules referencing surfaceflinger domain from public and
      vendor policies.
Bug: 31364497

Change-Id: I177751afad82ec27a5b6d2440cf0672cb5b9dfb8