Removed everything except the sources listed in CMakeLists.txt and files included by them
* Tests
* Build scripts
* Examples
* Non C++ sources

The only modification made is silencing warnings in headers included from src/server directories.

file config.h is completely custom that forces protobuf to emulate hash_* structures using std::set and std::map to avoid compatibility issues
otherwise it would be looking for old deprecated std::hash_set and std::hash_map and we would have to detect them based on platform