Clean up flag data_only_service_allow_emergency_call_only

The flag has been advanced to next for a long while and no regression is
observed. Clean it up the flag and TODO to keep the code healthy.

Bug: 296097429
Test: atest FrameworksTelephonyTests
Flag: EXEMPT flag clean up
Change-Id: I3cf41f284660ec37d7c638f06c1c8ed55e4ec746
1 file changed