Thanks for adding these details
These fields come from Migrated password hashes support.
So it’s not directly related to Discourse. The plugin can be safely uninstalled a while after a migration, when most members have logged in at least once. I don’t know if uninstalling the plugin keeps these fields or not. My guess is it shouldn’t keep them, but if it does, you could empty them from the rails console.
Sure, I’ll do that soon.
Edit: done.