Remove gogo vanity command and gogo dependency

[liggitt]

/hold for discussion

This repo has an example command that builds a vanity gogo proto generator. This results in passing along the (unmaintained, deprecated) gogo dependency to every downstream, even ones that don't use it. It doesn't look like the command or plugin has been touched in about ~8 years. (xref https://github.com/gogo/protobuf#deprecated-protocol-buffers-for-go-with-gadgets for deprecated status of that repo, and kubernetes/kubernetes#96564 for examples of downstreams trying to drop it out of dependency trees)

I can't find any use of the gogo command within containerd or kubernetes projects

There is some use I could find ... I'm a little fuzzy about what we'd recommend users do... switch to the protoc-gen-go-ttrpc generator? (the in-repo example seems to only be generated with the protoc-gen-go-ttrpc generator)

If users can switch to a standard generator with no impact, can we drop the gogo vanity command and this dependency? If dropping it would be problematic, could we move it to an example subfolder with its own isolating go.mod file to drop it out of the main module dependencies?

/cc @samuelkarp

[liggitt]

cc @dmcgowan

[fuweid]

LGTM

we stop using gogo since d240c50

[liggitt]

any chance of getting a tag containing these changes? That would help us ripple out dropping this dep from kubernetes and cadvisor (and containerd main in time for 2.4)