test: remove --experimental-worker flag comment

worker is stable in the master branch. The flag is no longer required.

PR-URL: #31563
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/test-worker-fs-stat-watcher.js

@@ -1,4 +1,3 @@
-// Flags: --experimental-worker
 'use strict';
 const common = require('../common');
 const { Worker, parentPort } = require('worker_threads');