Don't create system fixed, revoked permissions

.. when restricting a previously unrestricted permission.

Fixes: 134069814
Test: Upgraded from Q (before loc bg was restricted) to Q (after log bg
      was restricted) and saw previously system-fixed loc bg perm to be
      re-granted via the DefaultPermissionGrantPolicy.
Change-Id: I641a95a0e481ca057c4fb7e05b29b18b7a8c10b6