Move import lock onto backend (#2797)

* Drop import_lock from client, move it into backend, impl default version via static mutex

* still need to allow depcretion because of client.backend

* additional docs

* Remove default impl of get_import_lock, impl on instances

* Bump parking_lot to 0.8.0 accross the board

substrate/core/consensus/babe/Cargo.toml

@@ -24,7 +24,7 @@ slots = { package = "substrate-consensus-slots", path = "../slots"  }
 runtime_primitives = { package = "sr-primitives", path = "../../sr-primitives" }
 futures = "0.1.26"
 tokio = "0.1.18"
-parking_lot = "0.7.1"
+parking_lot = "0.8.0"
 log = "0.4.6"
 schnorrkel = "0.1.1"
 rand = "0.6.5"

substrate/core/consensus/babe/src/lib.rs

@@ -975,7 +975,7 @@ mod tests {
 
 
 			#[allow(deprecated)]
-			let select_chain = LongestChain::new(client.backend().clone(), client.import_lock().clone());
+			let select_chain = LongestChain::new(client.backend().clone());
 
 			let babe = start_babe(BabeParams {
 				config,