It was never used as we derive entropy via the other fields in the
transcript, and explicitly add fields directly as needed for entropy.
Also drops an unused crate and corrects a bug in FROST's Schnorr
implementation which used the Group's generator, instead of the Curve's.
Also updates the Monero crate's description.
Honestly, the borrowed keys are frustrating, and this probably reduces
performance while no longer offering an order when iterating. That said,
they enable full u16 indexing and should mildly improve the API.
Cleans the Proof of Knowledge handling present in key gen.
