Update travis test for registerRefundNotification

Author: Simon Schurter

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

@@ -1339,7 +1339,6 @@ public function testRegisterRefundNotification()
             ->willReturn($this->creditMemoMock);
         $this->creditMemoMock->expects($this->once())->method('setPaymentRefundDisallowed')->willReturnSelf();
         $this->creditMemoMock->expects($this->once())->method('setAutomaticallyCreated')->willReturnSelf();
-        $this->creditMemoMock->expects($this->once())->method('register')->willReturnSelf();
         $this->creditMemoMock->expects($this->once())->method('addComment')->willReturnSelf();
         $this->creditMemoMock->expects($this->once())->method('save')->willReturnSelf();
         $this->orderMock->expects($this->once())->method('getBaseCurrency')->willReturn($this->currencyMock);