resolvectl: use varlink to report delegate status

resolvectl: use varlink to report delegate status

This is an incremental commit to replacing dbus usage with varlink for
all status output.

Re-implement regular delegate status output using the DumpDNSConfiguration
varlink method. And, remove the DelegateInfo type and associated functions
which were used to map dbus properties.

Since this is the last type of status output to be switched to varlink,
lots of other code becomes dead with these changes, e.g.
read_dns_server_one(), map_dns_servers_internal(), etc., so remove those
too. Finally, status_all() no longer needs sd_bus, so drop that
parameter.