AI 144372: Cleanup Settings support for enabling and disabling location providers:

  LocationManagerService now listens for changes to settings,
  making LocationManager.updateProviders() unnecessary.
  Removed LocationManager.updateProviders()
  Added Settings.Secure.setLocationProviderEnabled(), which is a thread-safe way
  of enabling or disabling a single location provider.
  This is safer than reading, modifying and writing the LOCATION_PROVIDERS_ALLOWED directly.
  BUG=1729031

Automated import of CL 144372