Protos are duplicated

While reviewing #1500 and #1502 from @mahanteshwar-git, I noticed that:

https://github.com/etcd-io/jetcd/tree/main/jetcd-core/src/main/proto

seems to contain similar (or possibly [hopefully; not verified] identical) `*.proto` files to:

https://github.com/etcd-io/jetcd/tree/main/jetcd-grpc/src/main/proto

and was wondering what that was so... seems confusing (at least to me).

That `jetcd-grpc` module does not contain any other (Java) code.

@lburgazzoli do you know what the background story here is / was?

Was the intention here perhaps to build the proto in one module, and have the other (core) then depend on it - but it was left unfinished?