Expunged Monokex test vectors

Expunged Monokex test vectors

Monokex is unlikely to be added to Monocypher in the near future, for
a couple reasons:

- It is a high level protocol, and Monocypher is fairly low level.
- It is not yet ready for production.
- It takes a significant amount of code.

Maybe it will be added later, but first, Monokex must focus on being its
own library, with Monocypher as a dependency. (We could also have a
version that uses Libsodium instead.)