k256: remove implementation of PrehashSignature (#1275)

As discussed in RustCrypto/traits#1917

Author: carloskiki

Cargo.lock

@@ -20,5 +20,6 @@ members = [
 opt-level = 2
 
 [patch.crates-io]
+ecdsa = { git = "https://github.com/RustCrypto/signatures.git" }
 primefield = { path = "primefield" }
 primeorder = { path = "primeorder" }

Cargo.toml

@@ -12,6 +12,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Batch Normalization `normalizes_to_zero()` bug fix ([#1029])
 - Prevent panic when creating a Schnorr from slice ([#1056])
 
+### Removed
+- Implementation of `signature::PrehashSignature` on `schnorr::Signature` ([#1275])
+
 ## Changed
 - Update to `elliptic-curve` v0.14 ([#1011])
 - Update to `ecdsa` v0.17 ([#1011])