Removed OSU Provider APs of already provisioned Passpoint networks

Wifi picker should now not display an entry for an OSU Provider which
has already been used to provision a network.

Tracking bug for adding robolectric tests: b/122849296

Bug: 118705403
Test: none (yet)
Change-Id: Ifb1d6958d91e6bd4e53279cc27c72a81258a6fec