FIX: allows PM owner to remove any user if >= TL2 (PR #10036)

< TL2 user can remove itself: Screenshot 2020-06-12 at 10 35 50

= TL2 user can remove everyone: Screenshot 2020-06-12 at 10 35 58

GitHub

What happens if OP remove themselves from the PM? :thinking:

What happens if OP remove themselves from the PM? :thinking:

replaced by system user

Screenshot 2020-06-12 at 12 11 59

So we keep trace of the OP being crated by this user, but we replace its presence in the topic by system.