Grafana: Remove port numbers from "instance" label (again)

Recent changes to the monitoring code led to a regression where we now again have port numbers in the instance labels:

I suspect !236 (merged) or maybe !234 (merged). I thought I had tested and reviewed them thoroughly, and this didn't happen on my machine. Either this flew by my testing or it's a side effect of some other change.

/cc @tomprince since he was on some of this too, maybe you got a quick idea (if you are still here)