Clean up the fake user that the UserDirectory creates inside the current in-memory document when it is rendered

The UserDirectory uses a trick to properly display class property pretty names. For this, it creates an in-memory user object in the current document if the currently viewing user is not registered (is the guest user).

To avoid possible inconveniences (like making problems for code that checks if the current document is a user and renders the UserDirectory page for whatever reason), the fake user needs to be deleted from the in-memory document.