Remove duplicate JSResourceReferenceImpl mock (#25976)

This mock exists in 2 directories (with identical implementation) and
Jest just picks one at random. This removes one which makes it at least
deterministic and fixes a Jest warning on startup.

It existed in these 2 places:
-
`packages/react-server-dom-relay/src/__mocks__/JSResourceReferenceImpl.js`
-
`packages/react-server-native-relay/src/__mocks__/JSResourceReferenceImpl.js`
(removed)

packages/react-server-native-relay/src/__mocks__/JSResourceReferenceImpl.js

@@ -1,19 +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.
- */
-
-'use strict';
-
-class JSResourceReferenceImpl {
-  constructor(moduleId) {
-    this._moduleId = moduleId;
-  }
-  getModuleId() {
-    return this._moduleId;
-  }
-}
-
-module.exports = JSResourceReferenceImpl;