Due to our dependency on opentelemetry crates, protoc needs to be installed to use shuttle. This has been resolved in a recent release of the otel crates, but upgrading to those new versions is blocked by tracing-opentelemetry first getting updated. When tokio-rs/tracing-opentelemetry#12 is merged and released, we can go ahead and update the otel crates, removing the protoc requirement. The protoc prerequisite should also be removed from our docs.

We tried this too soon, so all the work has been done, #826 just needs to be reverted.