Update clearData flow for notification settings

Some settings need to be maintained (like whether the app
is the default dialer), so don't just wipe away all of the settings.

Test: atest; clear data on default dialer and ensure missed call
notification is still in priority bucket
Fixes: 127855529

Change-Id: I9e0c2fa1ceb371fe98a4f25f3573f043e9e2c1c9