Don't use Docker Links for user-defined networks

Docker Links are a deprecated feature.

For user-defined networks, they're silently ignored by the daemon, so we've been sending them regardless. Podman doesn't like this, and will fail with bad parameter: link is not supported.

Proposal

Client-side we should not send the container links if a user-defined network has been created. This also Runner created networks (which are still technically user-defined networks).