Silence known deprecation warnings (#2651)

* Silence known deprecation warnings

1. Prefixes known instances of usages of client.backend and client.import_lock with `#[allow(deprecated)]` to silence the warnings. 2. Remove file-global `#![allow(deprecated)]` used in these cases. Both to prevent us overlooking externally caused deprecation messages.

* fixing missing ;

* fix missing test cases

* move deprecated markers to make CI happy

* move deprecated markers to make CI happy

* attempt to fix the test

* bumping impl_version of node runtime

* Minor cleanup

substrate/core/service/src/components.rs

@@ -646,6 +646,7 @@ mod tests {
 			from: AccountKeyring::Alice.into(),
 			to: Default::default(),
 		}.into_signed_tx();
+		#[allow(deprecated)]
 		let best = LongestChain::new(client.backend().clone(), client.import_lock())
 			.best_chain().unwrap();