Restore compatibility with Symfony 4.x

[toth-dev]

Remove argument type added to onAuthenticationSuccess in f8b3a8a. Not having a type specified for the argument in the subclass is compatible with both versions, as it is more generic; while having the type is not compatible (has a more restricted signature than the overridden function) with the base class in 4.x causing this error:

Niif\ShibAuthBundle\Security\ShibbolethAuthenticator
::onAuthenticationSuccess(Symfony\Component\HttpFoundation\Request $request, Symfony\Component\Security\Core\Authentication\Token\TokenInterface $token, string $providerKey)
must be compatible with
Symfony\Component\Security\Guard\GuardAuthenticatorInterface
::onAuthenticationSuccess(Symfony\Component\HttpFoundation\Request $request, Symfony\Component\Security\Core\Authentication\Token\TokenInterface $token, $providerKey

See symfony/symfony@51b3c2e.