It is deprecated in C++17 because it isn't helpful and makes code more obfuscated. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0174r0.html#2.1

This would only break source-compatibility with code that foolishly uses std::is_base_of<std::iterator<...>, SOME_MONGO_TYPE>.