Revert "Open WiFi network when pull out the USB line."

This reverts commit adce6ee6.
- Tethering from WiFi to USB is a perfectly legit use case, nuke that
  shit.
- That extra xml key + check is useless and breaks USB tethering
  entirely unless added to the overlay.

Change-Id: I8c1c5d267a16df310f944234235234076787cd03