tools: delete an unused argument

PR-URL: https://github.com/nodejs/node/pull/14251
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>

tools/jslint.js

@@ -120,7 +120,7 @@ if (cluster.isMaster) {
 
   if (showProgress) {
     // Start the progress display update timer when the first worker is ready
-    cluster.once('online', function(worker) {
+    cluster.once('online', function() {
       startTime = process.hrtime();
       setInterval(printProgress, 1000).unref();
       printProgress();