build: remove unused gulp helper script (#50428)

We still seem to be having Gulp installed for the ZoneJS changelog
generation. Arguably this can be replaced with a simpler JS script,
but in either case, this commit removes an unused file from the old
Gulp task setup.

PR Close #50428

tools/gulp-tasks/platform-script-path.js

@@ -1,13 +0,0 @@
-/**
- * @license
- * Copyright Google LLC All Rights Reserved.
- *
- * Use of this source code is governed by an MIT-style license that can be
- * found in the LICENSE file at https://angular.io/license
- */
-
-// returns the script path for the current platform
-module.exports = function platformScriptPath(path) {
-  const os = require('os');
-  return /^win/.test(os.platform()) ? `${path}.cmd` : path;
-};