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/consensus/aura/src/lib.rs

@@ -1026,6 +1026,7 @@ mod tests {
 		let mut runtime = current_thread::Runtime::new().unwrap();
 		for (peer_id, key) in peers {
 			let client = net.lock().peer(*peer_id).client().as_full().expect("full clients are created").clone();
+			#[allow(deprecated)]
 			let select_chain = LongestChain::new(
 				client.backend().clone(),
 				client.import_lock().clone(),