Delete `rules_rust_protobuf`

[UebelAndre]

rules_rust_protobuf in my years of maintainer-ship on this repo has never had a clear owner. In an effort to clean out dead code within the repo, I think this should probably be deleted given the end-of-life messaging on the upstream repo.

If anyone is actively using these rules please make yourself known and explain why prost isn't an appropriate alternative.

Thanks!

[UebelAndre]

It also looks like protobuf is finally documenting the existence of rust support upstream: https://protobuf.dev/reference/rust/