auth_user in EVENT_SINK_PII_MODELS errors on retirement

[bmtcril]

While investigating other issues I ran into one which I think we've seen before where having auth_user in the EVENT_SINK_PII_MODELS configuration list causes retirement to fail when it tries to delete the user from a table that doesn't exist. I don't believe we need that model there, but need more time to investigate it or input from @pomegranited on why we did that. I'd like to just remove it, but this task is to spend some time reviewing where it's used before we do that.