Remove rng_seed's additional entropy

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.

crypto/frost/Cargo.toml

@@ -14,7 +14,6 @@ rand_core = "0.6"
 ff = "0.11"
 group = "0.11"
 
-blake2 = "0.10"
 transcript = { path = "../transcript" }
 
 multiexp = { path = "../multiexp", features = ["batch"] }

crypto/frost/src/algorithm.rs

@@ -73,7 +73,7 @@ impl Transcript for IetfTranscript {
     self.0.clone()
   }
 
-  fn rng_seed(&mut self, _: &'static [u8], _: Option<[u8; 32]>) -> [u8; 32] {
+  fn rng_seed(&mut self, _: &'static [u8]) -> [u8; 32] {
     unimplemented!()
   }
 }

crypto/frost/src/schnorr.rs

@@ -1,7 +1,6 @@
 use rand_core::{RngCore, CryptoRng};
 
 use ff::Field;
-use group::Group;
 
 use multiexp::BatchVerifier;
 
@@ -46,7 +45,7 @@ pub(crate) fn batch_verify<C: Curve, R: RngCore + CryptoRng>(
   rng: &mut R,
   triplets: &[(u16, C::G, C::F, SchnorrSignature<C>)]
 ) -> Result<(), u16> {
-  let mut values = [(C::F::one(), C::G::generator()); 3];
+  let mut values = [(C::F::one(), C::generator()); 3];
   let mut batch = BatchVerifier::new(triplets.len(), C::little_endian());
   for triple in triplets {
     // s = r + ca