Go: Remove go.work file

[mbg]

This (once again) removes the go.work file from the repository. Our main motivation for having it was that gopls (which is used by the Go extension for VSCode) seemed to require having one for some time, but now:

• It turns out that Dependabot does not support Go workspaces.
• The Go documentation advises against committing go.work files now.
• gopls no longer seems to require a go.work file to work correctly.

[owen-mc]

We should check with @redsun82 whether any changes are needed to the bazel build system. For example, I just came across the fact that go/gen.py runs go work vendor to update the vendor directory (on line 51).

[mbg]

Yep it seems like that breaks now in CI

[redsun82]

I think that was the way I found to vendor dependencies without using -m vendor in compilation when the go.work file was around, but what @mbg is doing with go mod vendor seems the way to go (there's just a small diff to apply removing the workspace comment`)

[mbg]

@owen-mc looks fine now

[owen-mc]

Seems to work on my machine