Removed unnecessary protected member variables.

Removed unnecessary protected member variables of Image class.
The variable `$imageHelper`, `$product` and `$attributes` are not in use.
Above three variable doesn't contain any values. Also verified it on category, product and cart page.

Author: yogeshks

app/code/Magento/Catalog/Block/Product/Image.php

@@ -19,21 +19,6 @@
  */
 class Image extends \Magento\Framework\View\Element\Template
 {
-    /**
-     * @var \Magento\Catalog\Helper\Image
-     */
-    protected $imageHelper;
-
-    /**
-     * @var \Magento\Catalog\Model\Product
-     */
-    protected $product;
-
-    /**
-     * @var array
-     */
-    protected $attributes = [];
-
     /**
      * @param \Magento\Framework\View\Element\Template\Context $context
      * @param array $data