[Provider Model] Preferences Settings UI change

- Change the title from “Wi-Fi preference” to “Preferences”
- Change the summary from “Wi-Fi turns back on automatically” to
“Connect to public networks”
- Remove “Turn on Wi-Fi automatically” preference
- Screenshot:
  https://screenshot.googleplex.com/Areywyb46deK9VQ
  https://screenshot.googleplex.com/6H5Z4PxA5tWXZ6S

Bug: 172788645
Test: manual test
Change-Id: Ibce21f1d740a139b407a0a9a41f2cb4c4e34776c