Squashed 'extern/protobuf/' content from commit d6e20ba

git-subtree-dir: extern/protobuf
git-subtree-split: d6e20baabb84501c720b6e42170684264bd2cdd2
Merge commit '6030ebbb2a6fe7a2688696f3029edce6b64b8ae1' as 'extern/protobuf'
Remove previous protobuf tree
[WIP] move protobuf to unity dir