message: [types] fix warning
  Closes:
diff: // SPDX-License-Identifier: Apache-2.0
  use crate::{account_address::AccountAddress, on_chain_config::ValidatorSet};
  -use anyhow::{ensure, Result};
  use libra_crypto::{
  ed25519::{Ed25519PublicKey, Ed25519Signature},
  hash::CryptoHash,
  Signature, VerifyingKey,
  };
  -#[cfg(any(test, feature = "fuzzing"))]
  -use proptest_derive::Arbitrary;
  use serde::{Deserialize, Serialize};
  use std::{collections::BTreeMap, fmt};
  use thiserror::Error;
  +#[cfg(any(test, feature = "fuzzing"))]
  +use anyhow::{ensure, Result};
  +#[cfg(any(test, feature = "fuzzing"))]
  +use proptest_derive::Arbitrary;
  +
  /// Errors possible during signature verification.
  #[derive(Debug, Error, PartialEq)]
  pub enum VerifyError {
  