Fix for unit test

Author: ivanko-dev

app/code/Magento/Quote/Test/Unit/Model/QuoteManagementTest.php

@@ -576,7 +576,6 @@ public function testAssignCustomer()
         $cartId = 220;
         $customerId = 455;
         $storeId = 5;
-        $activeQuoteMock = null;
 
         $this->getPropertyValue($this->model, 'quoteIdMaskFactory')
             ->expects($this->once())