As of new EU regulations, we probably need to remove the user's Log entries when a User is deleted.

I think this should happen in the UserInfo class, along with these lines:
https://github.com/concrete5/concrete5/blob/658dc94e3892544e581f264c467325384f3fc36a/concrete/src/User/UserInfo.php#L225-L229

Edit: to do this in pre 8.4.0 releases I added a feature to the GDPR package: https://www.concrete5.org/marketplace/addons/gdpr/