After uninstalling FlaggedRevs, Special:ListUsers still shows users are in groups autoreview, editor and reviewer - although in plain text and no longer as links. How to remove these from the User list?
Topic on Extension talk:FlaggedRevs
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.