Revert "AC-14431: Order items order_date wrong formatting"

This reverts commit 5f3d640.

Author: glo60612

app/code/Magento/SalesGraphQl/Model/Formatter/Order.php

@@ -49,7 +49,7 @@ public function format(OrderInterface $orderModel): array
             'increment_id' => $orderModel->getIncrementId(),
             'number' => $orderModel->getIncrementId(),
             'order_date' => $this->timezone->date($orderModel->getCreatedAt())
-                ->format('d/m/Y H:i:s'),
+                ->format(DateTime::DATETIME_PHP_FORMAT),
             'order_number' => $orderModel->getIncrementId(),
             'status' => $orderModel->getStatusLabel(),
             'email' => $orderModel->getCustomerEmail(),