Move bluetoothdomain policy to private

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

Test: No change to policy according to sesearch, except for
      disappearance of all allow bluetoothdomain bluetooth_current
      rule (as expected).
Bug: 31364497

Change-Id: I0edfc30d98e1cd9fb4f41a2900954d9cdbb4db14