Remove client.backend (#2960)

* generalize tree_root to remove client.backend dependency

* replace client.backend.blockchain.header with client.header

* move used_state_cache_size into client info

* Create intermediate Setup State. Fixes #1134

* remove client.backend from finality proof

* update node-template

* move memory backend into test helper mode

* move test helper into client

* starting the big refactor, remove unused functions

* apply_finality

* apply_finality

* replacing more .backend from environment with client directly

* remove .backend from grandpa by using traits

* remove .backend from babe

* remove .backend from tests where it is not needed

* remove .backend from tests

* fixing tests

* fixing tests

* fixing more tests

* fixing tests

* fix all forks test

* fix style

* fixing unnecessary allocation

* remove old test.

* fix service docs

* apply suggestion

* minor clean ups

* turns out the test-helper features actually is being used!

* fixing line length.

* fix line length

* minor cleaning

* Apply suggestions from code review

thanks, @Basti

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* address grumbles

* simplify finalize block on client

* move block back into inner function

* Apply suggestions from code review

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* use as.ref instead of match

* Update core/client/src/backend.rs

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

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

@@ -857,8 +857,7 @@ impl<B, E, Block, RA, PRA, T> Verifier<Block> for BabeVerifier<B, E, Block, RA,
 				// chain.
 				let new_best = {
 					let (last_best, last_best_number) = {
-						#[allow(deprecated)]
-						let info = self.client.backend().blockchain().info();
+						let info = self.client.info().chain;
 						(info.best_hash, info.best_number)
 					};
 
@@ -1321,8 +1320,7 @@ impl<B, E, Block, I, RA, PRA> BlockImport<Block> for BabeBlockImport<B, E, Block
 
 		// early exit if block already in chain, otherwise the check for
 		// epoch changes will error when trying to re-import an epoch change
-		#[allow(deprecated)]
-		match self.client.backend().blockchain().status(BlockId::Hash(hash)) {
+		match self.client.status(BlockId::Hash(hash)) {
 			Ok(blockchain::BlockStatus::InChain) => return Ok(ImportResult::AlreadyInChain),
 			Ok(blockchain::BlockStatus::Unknown) => {},
 			Err(e) => return Err(ConsensusError::ClientImport(e.to_string()).into()),
@@ -1496,8 +1494,7 @@ pub fn import_queue<B, E, Block: BlockT<Hash=H256>, I, RA, PRA, T>(
 		transaction_pool,
 	};
 
-	#[allow(deprecated)]
-	let epoch_changes = aux_schema::load_epoch_changes(&**client.backend())?;
+	let epoch_changes = aux_schema::load_epoch_changes(&*client)?;
 
 	let block_import = BabeBlockImport::new(
 		client.clone(),