Thread:Extension talk:FlaggedRevs/Uninstallation/reply

I don't know of any script to remove user groups. If you don't care about adding user rights log entries, then you can start maintenance/sql.php and issue a SQL statement like "DELETE FROM user_groups WHERE ug_group IN ('editor','reviewer','autoreview')". If there are many users you may want to add "LIMIT 100" to the end and keep running it until there are 0 affected rows.