Move mobile provisioning APN support into telephony.

Most of this logic is simply removed from ConnectivityService.
The captive portal detection is now done by the NetworkMonitor.
The notification logic is still left in ConnectivityService as
it's used by both the NetworkMonitor and telephony's mobile
provisioning logic.

bug:17324098

Change-Id: Ibd1c42b1a75795f90a6483d3d0a5a14f88b193d8