Remove findDOMNode www shim (#25998)

This shim is no longer needed on www, in fact I had already deleted it
there and it's currently not on www. See D42503692 which is trying to
add it back as I didn't realize this file was synced from GitHub.

scripts/rollup/shims/facebook-www/findDOMNode.js

@@ -1,15 +0,0 @@
-/**
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *
- * @flow
- * @format
- */
-
-'use strict';
-
-const {findDOMNode} = require('ReactDOM');
-
-module.exports = findDOMNode;