test/dbus-daemon: Mark max-connections-per-user as unimplemented on Windows
The implementation of the max-connections-per-user limit works in terms of Unix uids, so it doesn't apply on Windows.
This is not a problem in practice, because it only makes sense to limit connections per user if you have multiple users, and we don't support the well-known system bus on Windows.
This is loosely based on part of !23 (merged), and is untested. @rhabacker, perhaps you could test this?
Edited by Simon McVittie