SessionStorage: Fix clearing identity in case of clearAuthentication(true).

[janbarasek]

• bug fix
• BC break? yes

User defined code (for logout function):

$this->userStorage->clearAuthentication(true);
$this->userStorage->setExpiration(null, true);

Mark user as unauthenticated, but an original identity kept stored in Session. I think when clearAuthentication(true) the identity must be removed.

[dg]

Thanks