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>

cumulus/parachain-template/node/src/rpc.rs

@@ -9,7 +9,7 @@ use std::sync::Arc;
 
 use parachain_template_runtime::{opaque::Block, AccountId, Balance, Nonce};
 
-pub use sc_rpc::{DenyUnsafe, SubscriptionTaskExecutor};
+pub use sc_rpc::DenyUnsafe;
 use sc_transaction_pool_api::TransactionPool;
 use sp_api::ProvideRuntimeApi;
 use sp_block_builder::BlockBuilder;