Remove outdated ML-DSA versions

[marsella]

We have several old versions of ML-DSA (from the PQ competition, when it was CRYSTALS-Dilithium, and from the initial public draft of FIPS-204). We should remove those, although we can keep a link to the commit that deleted them as in ECDSA.

• Remove Round 1, Round 2, and "Final Draft" ML-DSA versions
• Update ML-DSA README to reflect the current state of the implementation and link to deleted versions
• Update top-level readme to correctly indicate which versions are available.