Revert "[Security] Missing Event namespace in SwitchUserListener"

This reverts commit 0169892dcd7f3c5549f7dcbcf0bde9bbadcda525.

src/Symfony/Component/Security/Http/Firewall/SwitchUserListener.php

@@ -17,7 +17,6 @@ use Symfony\Component\Security\Core\User\UserProviderInterface;
 use Symfony\Component\Security\Core\User\AccountCheckerInterface;
 use Symfony\Component\Security\Core\Authorization\AccessDecisionManagerInterface;
 use Symfony\Component\HttpKernel\Log\LoggerInterface;
-use Symfony\Component\EventDispatcher\Event;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use Symfony\Component\EventDispatcher\EventInterface;
 use Symfony\Component\Security\Core\Exception\AuthenticationException;