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/node-template/src/service.rs

@@ -129,6 +129,7 @@ construct_service_factory! {
 			},
 		SelectChain = LongestChain<FullBackend<Self>, Self::Block>
 			{ |config: &FactoryFullConfiguration<Self>, client: Arc<FullClient<Self>>| {
+				#[allow(deprecated)]
 				Ok(LongestChain::new(
 					client.backend().clone(),
 					client.import_lock()