Is your feature request related to a problem? Please describe.
Yes, I accidentally misspelt a player name and it has made an entry in the /perm user [USERNAME] command and I have found no way to remove it.

Describe the solution you'd like
I would like a command that allows you to remove users from /perm user because it is kind of inconvenient to have to manually edit the permissions.json file and potentially break something.

Describe alternatives you've considered
Editing the JSON file and manually removing the user.

Additional context
For example, a /perm user [USERNAME] delete command to delete the user in /perm

Deleting groups/users is considered an advanced topic and thus was never implemented in the command. That is why you can only remove things manually in the json.

However, I am am willing to give it another look to see if that functionality could be added into the command.