Remove protoc installation instruction

This is now handled by scripts/install_build_tools.sh.

scripts/protobuf_setup.md

@@ -1,6 +0,0 @@
-# Setup
-
-You need to install protoc (protobuf compiler) and protoc-gen-go.
-
-- For protoc-gen-go just simple install by `go get -u github.com/golang/protobuf/protoc-gen-go`
-- For protoc, you install from the release https://github.com/protocolbuffers/protobuf/releases.