Parameter xwiki.authentication.unauthorized_code is not taken into account

The parameter xwiki.authentication.unauthorized_code has been removed from the default xwiki.cfg in the frame of XWIKI-11038. However MyFormAuthenticator.java still parses this parameter and the User Authentication documentation page still has a reference to it. This issue it to check why it is not taken into account or if it is in some condition and what should be done with this parameter.