Warning: removing users from the database may cause errors if these users are authors of tickets, or of anything else (which is the case if they were imported from a Trac database).
It would only be a good idea if user doesn't have any related object, which must be quite rare. For the import case, we could accept you have to do some actions in console, or we could improve import script.
As the issue is inactive for 2 years, I close it and encourage you to file new feature requests so we could improve user locking if needed.
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