Relaxed clippy fixes/nits (#2661)

This PR contains just a few clippy fixes and nits, which are, however,
relaxed by workspace clippy settings here:
https://github.com/paritytech/polkadot-sdk/blob/master/Cargo.toml#L483-L506

---------

Co-authored-by: Dmitry Sinyavin <dmitry.sinyavin@parity.io>
Co-authored-by: ordian <write@reusable.software>
Co-authored-by: command-bot <>
Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/frame/beefy/src/mock.rs

@@ -37,10 +37,7 @@ use sp_state_machine::BasicExternalities;
 
 use crate as pallet_beefy;
 
-pub use sp_consensus_beefy::{
-	ecdsa_crypto::{AuthorityId as BeefyId, AuthoritySignature as BeefySignature},
-	ConsensusLog, EquivocationProof, BEEFY_ENGINE_ID,
-};
+pub use sp_consensus_beefy::{ecdsa_crypto::AuthorityId as BeefyId, ConsensusLog, BEEFY_ENGINE_ID};
 
 impl_opaque_keys! {
 	pub struct MockSessionKeys {