fix: remove redundant error check for PubKeyToProto (#4917)

I don't see this on main branch, so this is just a patch for v0.38.x

---

#### PR checklist

- [ ] Tests written/updated
- [ ] Changelog entry added in `.changelog` (we use
[unclog](https://github.com/informalsystems/unclog) to manage our
changelog)
- [ ] Updated relevant documentation (`docs/` or `spec/`) and code
comments

Author: islishude

privval/signer_requestHandler.go

@@ -36,10 +36,6 @@ func DefaultValidationRequestHandler(
 			return res, err
 		}
 		pk, err := cryptoenc.PubKeyToProto(pubKey)
-		if err != nil {
-			return res, err
-		}
-
 		if err != nil {
 			res = mustWrapMsg(&privvalproto.PubKeyResponse{
 				PubKey: cryptoproto.PublicKey{}, Error: &privvalproto.RemoteSignerError{Code: 0, Description: err.Error()}})