MediaWiki:Maintenance-removeUnusedAccounts
An unused account is one which has no edits, no deleted edits, no log entries (task T36581) and no current/old uploads. You can use deleteArchivedRevisions.php to first remove deleted revisions (e.g. after a massive vandalism/spam attack) and run removeUnusedAccounts.php afterwards.
With no check box selected it just list the unused account.