cert-request: remove allowed extensions check
    
    cert-request currently permits a limited number of request
    extensions; uncommon and esoteric extensions are prohibited and this
    limits the usefulness of custom profiles.
    
    The Dogtag profile has total control over what goes into the final
    certificate and has the option to reject request based on the
    request extensions present or their values, so there is little
    reason to restrict what extensions can be used in FreeIPA.  Remove
    the check.
    
    Fixes: https://fedorahosted.org/freeipa/ticket/5205
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>