protoc-gen-hack/plugin.go was generating the gzipped binary
ProtoDescriptorProto and returning it to protoc so we could
save it to a file. protoc was warning us about having those
file's content being invalid UTF-8.

Unfortunately newer protoc binary reject files with such a
ayload. We do want to keep the binary FileDescriptorProto
logic for servers that can send the binary descriptor to
their clients but we can inline it in each generated file.

While we don't need to gzip the content anymore, I kept
this logic as we were generating large binary strings
in Hacklang.

…y_proto