As part of the major tethering refactor to associate every IpServer with
a TetheringRequest, tether()/untether() APIs should be completely
removed in B and all tethering should go through startTethering() (with
the exception of Wifi LOHS and Wifi P2P, which will move to
startTethering() in a future CL).
Bug: 216524590
Test: atest CtsTetheringTests TetheringTests
Change-Id: If7981f1ee7d80ff0a1cc0069ba7a4ebf79144160
30d8a25db3