Various nits and alignments for testnet runtimes (#3024)

There were several improvements and PRs that didn't apply to all
runtimes, so this PR attempts to align those small differences. In
addition, the PR eliminates unused dependencies across multiple modules.

Relates to PR for `polkadot-fellows`:
https://github.com/polkadot-fellows/runtimes/pull/154

substrate/bin/node-template/runtime/src/lib.rs

@@ -310,13 +310,9 @@ pub type Executive = frame_executive::Executive<
 	Migrations,
 >;
 
-#[cfg(feature = "runtime-benchmarks")]
-#[macro_use]
-extern crate frame_benchmarking;
-
 #[cfg(feature = "runtime-benchmarks")]
 mod benches {
-	define_benchmarks!(
+	frame_benchmarking::define_benchmarks!(
 		[frame_benchmarking, BaselineBench::<Runtime>]
 		[frame_system, SystemBench::<Runtime>]
 		[pallet_balances, Balances]