New pref toggle for network recommendations.

Adding a new toggle to control whether network
recommendations are enabled.

Removed the "Use open networks" pref and its associated strings
and components as it's no longer needed.

Test: Built and ran.
BUG: 33549591
BUG: 33270391
Change-Id: I7248ac32e0598d82107c150372c1fe4e9e2243a5