Remove calls to setRoaming.

There are no users left of this method or the member it sets.
ConnectivityService is taking this information from the
NetworkCapabilities, and the capabilities sent by DataConnection
read it from mPhone.getServiceState().getDataRoaming().

Bug: 138306002
Test: FrameworksTelephonyTests
Change-Id: Id48c1584d7a3fcc1511a68fa40bcca695947fcdb