Manual:$wgNewUserLog

Details
Whether to maintain a log of newusers at Special:Log/newusers.

When set to true (default)...
 * users will be able to access Special:Log/newusers to see new user registrations on your wiki. These events will also appear on you Recent Changes page.

When set to false...
 * Special:Log/newusers will report "No matching items in log". This can help to declutter your Recent Changes display.
 * Note: These kinds of log entry can alternatively be decluttered substantially by using Enhanced recent changes which folds them into one line.

Replaces , that extension is now obsolete.