Remove the menu link via the admin interface, then remove the file qa-page-users.php so that people entering the users URL directly still won't be able to see the user list.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.