Remove some more legacy code

Author: nicolas-grekas

Security/User/EntityUserProvider.php

@@ -55,11 +55,7 @@ public function loadUserByUsername($username)
             $user = $this->repository->findOneBy(array($this->property => $username));
         } else {
             if (!$this->repository instanceof UserLoaderInterface) {
-                if (!$this->repository instanceof UserProviderInterface) {
-                    throw new \InvalidArgumentException(sprintf('The Doctrine repository "%s" must implement Symfony\Bridge\Doctrine\Security\User\UserLoaderInterface.', get_class($this->repository)));
-                }
-
-                @trigger_error('Implementing loadUserByUsername from Symfony\Component\Security\Core\User\UserProviderInterface is deprecated since version 2.8 and will be removed in 3.0. Implement the Symfony\Bridge\Doctrine\Security\User\UserLoaderInterface instead.', E_USER_DEPRECATED);
+                throw new \InvalidArgumentException(sprintf('The Doctrine repository "%s" must implement Symfony\Bridge\Doctrine\Security\User\UserLoaderInterface.', get_class($this->repository)));
             }
 
             $user = $this->repository->loadUserByUsername($username);