Scripts and documentation still refer to pre-Go-module practices

Almost anything that references `GOPATH/src` is from prior to go modules being fully adopted. It used to be that having all go code in that directory was expected (required?). Now it is only there if users go out of their way to check out code there.

I'm working on cleaning up the easy references to this, but there will be a long tail that might take some time to tidy up as they are deep in scripts that haven't been run in some time (e.g. scripts for running on public GCP).