graphQl-533: removed redundant import

Author: Vitaliy Boyko

dev/tests/api-functional/testsuite/Magento/GraphQl/Quote/Guest/SetPaymentMethodOnCartTest.php

@@ -10,7 +10,6 @@
 use Magento\GraphQl\Quote\GetMaskedQuoteIdByReservedOrderId;
 use Magento\OfflinePayments\Model\Cashondelivery;
 use Magento\OfflinePayments\Model\Checkmo;
-use Magento\OfflinePayments\Model\Purchaseorder;
 use Magento\TestFramework\Helper\Bootstrap;
 use Magento\TestFramework\TestCase\GraphQlAbstract;