MAGETWO-60054: Revert major changes in PaymentAdapter

fix tests

Author: valdislav

app/code/Magento/Sales/Test/Unit/Model/Order/PaymentAdapterTest.php

@@ -25,11 +25,6 @@ class PaymentAdapterTest extends \PHPUnit_Framework_TestCase
      */
     private $creditmemoMock;
 
-    /**
-     * @var \Magento\Sales\Model\Order\Creditmemo\RefundOperation|\PHPUnit_Framework_MockObject_MockObject
-     */
-    private $refundOperationMock;
-
     /**
      * @var \Magento\Sales\Api\Data\InvoiceInterface|\PHPUnit_Framework_MockObject_MockObject
      */