Remove unused imports

Author: alexandre-daubois

Tests/Event/FailedMessageEventTest.php

@@ -20,7 +20,6 @@
 use Symfony\Component\Notifier\Message\SmsMessage;
 use Symfony\Component\Notifier\Tests\Transport\DummyMessage;
 use Symfony\Component\Notifier\Transport\AbstractTransport;
-use Symfony\Component\Notifier\Transport\NullTransport;
 use Symfony\Contracts\EventDispatcher\EventDispatcherInterface;
 use Symfony\Contracts\HttpClient\HttpClientInterface;