You can simply delete accounts from the table usermanually, or at least disable their credentials using a query, for example:
UPDATE user SET
user_password = '',
user_newpassword = '',
user_email = '',
user_token = ''
WHERE
(Replace /*_*/with $wgDBprefix, if any. Oh, and backup first.)
user_password user_newpassword . user_email , user_token , .
:. , MediaWiki. , ( , , , rebuildall.php ) Webmasters Stack Exchange.
Extension:RegexBlock:
"RegexBlock - , , IP- ".