Don't save configs

There is not actually any great reason to use couch session
logins in npm registries.  It's aggressively weird when couch
is actually multiple different couches behind a load balancer.
Remove couchLogin

This isn't really very effective when the registry is actually multiple
different CouchDB instances.  And, it's not any more secure, really, than
just sending the username and password.
v0.3.6