MAGETWO-86748: Fix: remove TestObserver class #13174

 - Merge Pull Request magento/magento2#13174 from Coderimus/magento2:legacy/remove-test-controller
 - Merged commits:
   1. 7af2391c

app/code/Magento/ProductAlert/Controller/Add/TestObserver.php

-<?php
-/**
- * Copyright © Magento, Inc. All rights reserved.
- * See COPYING.txt for license details.
- */
-namespace Magento\ProductAlert\Controller\Add;
-
-use Magento\ProductAlert\Controller\Add as AddController;
-use Magento\Framework\DataObject;
-
-class TestObserver extends AddController
-{
-    /**
-     * @return void
-     */
-    public function execute()
-    {
-        $object = new DataObject();
-        /** @var \Magento\ProductAlert\Model\Observer $observer */
-        $observer = $this->_objectManager->get(\Magento\ProductAlert\Model\Observer::class);
-        $observer->process($object);
-    }
-}