Remove a querystring parameter to fix v12.2 backups.

In the v10 backup routine, we were passing "type=backup" as part of
the querystring in addition to POSTing it. This was causing a problem
with one v12.2 host, and that's why I'm just going to blame v12.2 for
the problem. It looks like the querystring parameter is not needed for
any of the other versions/hosts that I've tested against.