Cleanup flag add_anomaly_when_notify_config_changed_with_invalid_phone

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

Bug: 270757342
Test: m -j
Flag: EXEMPT aconfig flag clean up only
Change-Id: I5e556579b468e4fb175a60e0fdb7df52fc391aeb