Revert setting sessionMaxAge for old clients
    
    Older clients have issues properly parsing cookies and the sessionMaxAge
    setting is one of those that breaks them.
    Comment out the setting and add a comment that explains why it is not
    set by default.
    
    https://pagure.io/freeipa/issue/7001
    
    Signed-off-by: Simo Sorce <simo@redhat.com>
    Reviewed-By: Pavel Vomacka <pvomacka@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>