Remove all knowledge of tethering from SoftApManager

This logic has moved into Tethering and TetherInterfaceStatemachine,
where it probably always belonged.

Bug: 29054780
Test: WiFi tethering continues to work on angler
      `runtest frameworks-wifi` passes.

Change-Id: Ifff78ea540929fde4abea65716e1f659da2ecfec
3 files changed
tree: 1899c2f142beebbb733a5a8d55086a70c1c6de33
  1. service/
  2. tests/