test: remove unused parameter

PR-URL: #17184
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: fdescamps

test/sequential/test-readline-interface.js

@@ -97,9 +97,7 @@ FakeInput.prototype.end = () => {};
       crlfDelay
     });
     let callCount = 0;
-    rli.on('line', function(line) {
-      callCount++;
-    });
+    rli.on('line', () => callCount++);
     fi.emit('data', '\r');
     setTimeout(common.mustCall(() => {
       fi.emit('data', '\n');