Decouple WFC roaming setting from roaming status

The WFC roaming setting should not be dependent on
the current roaming status. Remove the shortcut that
would automatically disable wfc roaming if on the
home network.

Bug: 131267855
Test: atest FrameworksTelephonyTests:ImsManagerTest
Change-Id: Iabb2a3b39f34252616b30add88a546f620e65825