Bogus note in [fs.path.native.obs]

[jwakely]

[Note 1 : Conversion to string_type is provided so that an object of class path can be given as an argument to existing standard library file stream constructors and open functions. — end note]

This was true for std::experimental::filesystem::path but not for std::filesystem::path, because std::basic_filebuf etc. support construction from a path directly. The conversion operator probably doesn't need to exist at all in the IS, but we can't fix that now. We can at least remove the bogus note.