Remove unused BilletOrder import from OrderControllerTest

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/Controller/OrderControllerTest.php

@@ -5,7 +5,6 @@ namespace App\Tests\Controller;
 use App\Entity\Billet;
 use App\Entity\BilletBuyer;
 use App\Entity\BilletBuyerItem;
-use App\Entity\BilletOrder;
 use App\Entity\Category;
 use App\Entity\Event;
 use App\Entity\User;