docs: use JavaScript based PolicyKit .rules files

docs: use JavaScript based PolicyKit .rules files

PolicyKit authentication rules have switched to a JavaScript based
format quite some time ago. See:

http://davidz25.blogspot.com/2012/06/authorization-rules-in-polkit.html

While backwards compat for the old .pkla format is still available, it
makes sense to point people first at the new format.

The SSHPolicyKitSetup wiki page seems pretty stale, so remove the
reference to it.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Mark McLoughlin <markmc@redhat.com>