Clean up flag show_call_id_and_call_waiting_in_additional_settings_menu

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

Bug: 310264981
Test: atest FrameworkTelephonyTests and CtsTelephonyTestCases
Flag: EXEMPT flag clean up
Change-Id: Ia640b9bdb79d3e79908321aeef01811ab955e057