[Passpoint] Clear T&C URL post verification

Clear the Passpoint T&C URL after the state machine
receives a VALIDATION_STATUS_VALID message, which means that
the user accepted the T&Cs and internet access is available.

Bug: 162785447
Test: End to end test
Test: atest ClientModImplTest PasspointManagerTest
Change-Id: Iba521c5bc175b9a1a27d9277c236fd5a4fff72cc
4 files changed