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

Test: Device boot, apps (untrusted_app, system_app, platform_app,
      priv_app) work fine. No new denials.
Bug: 31364497

Change-Id: Ie22e35bad3307bb9918318c3d034f1433d51677f