Remove unnecessary CofactorGroup documentation

Author: AaronFeickert

curve25519-dalek/src/edwards.rs

@@ -1589,7 +1589,6 @@ impl GroupEncoding for SubgroupPoint {
 #[cfg(feature = "group")]
 impl PrimeGroup for SubgroupPoint {}
 
-/// Ristretto has a cofactor of 1.
 #[cfg(feature = "group")]
 impl CofactorGroup for EdwardsPoint {
     type Subgroup = SubgroupPoint;