browser config: cleanup after removal of Firefox extension
    
    Firefox extension which served for configuring Kerberos auth in Firefox
    until version which banned self-signed extensions was removed in commit
    6c53765ac1746ea3cb82554775a37fe43af062e8.
    
    Given that configure.jar, even older Firefox config tool, was removed
    sometime before that, there is no use for signtool tool. It is good
    because it is removed from Fedora 27 anyway. So removing last unused
    function which calls it.
    
    The removal of FF extension was not exactly clean so removing also
    browserconfig.html which only purpose was to use the extension. Therefore
    also related JS files are removed. This removal requires unauthorized.html
    to be updated so that it doesn't point to non-existing page. And given that
    it now points only to single config page, we can change link in UI login page
    to this page (ssbrowser.html). While at it, improving buttons in ssbrowser.html.
    
    Btw, commit 6c53765ac1746ea3cb82554775a37fe43af062e8 removed also generation of
    krb.js. It had one perk - with that info ssbrowser.html could display real
    Kerberos domain instead of only 'example.com'.  I don't have time to revert this
    change so removing traces of krb.js as well.
    
    https://pagure.io/freeipa/issue/7135
    
    Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>