As TetheringManager moves to a Public API, remove the weak
WRITE_SETTINGS permission and use TETHER_PRIVILEGED instead. System
callers can still aquire TETHER_PRIVILEGED, and public callers must be
Device Owner or Carrier App to bypass (to be done in a future CL)
Bug: 374400379
Test: atest TetheringTest TetheringServiceTest CtsTetheringTests
Change-Id: Ia192021ac48f9eb3f27cc8c412f17629ad16a587