Update EntityUserProvider.php

Fix Issue #429 - use statement should not contain reference to FOS and should maintain compatibility with Symfony\Component\Security\Core\User\UserProviderInterface.

Causes:
FatalErrorException: Compile Error: Declaration of HWI\Bundle\OAuthBundle\Security\Core\User\EntityUserProvider::refreshUser() must be compatible with Symfony\Component\Security\Core\User\UserProviderInterface::refreshUser(Symfony\Component\Security\Core\User\UserInterface $user)
when trying to initialize a user provider extending EntityUserProvider and implementing UserProviderInterface