cargo check warning with "--no-default-features"

[jku]

cargo check --no-default-features complains like this:

warning: method `verify_prehash` is never used
   --> src/crypto/verification_key.rs:334:19
    |
124 | impl CosignVerificationKey {
    | -------------------------- method in this implementation
...
334 |     pub(crate) fn verify_prehash(&self, signature: Signature, msg: &[u8]) -> Result<()> {
    |                   ^^^^^^^^^^^^^^
    |
    = note: `#[warn(dead_code)]` on by default

This happens on CI in the check-wasm job so all runs have an annoying annotation about this. I'm not sure what the correct fix is so just am just filing this issue.