Directly use the new `to_memory_db` function (#1080)

This reduces the amount of code a little bit.

cumulus/pallets/parachain-system/src/validate_block/implementation.rs

@@ -66,19 +66,15 @@ where
 	let block = B::new(header, extrinsics);
 	assert!(parent_head.hash() == *block.header().parent_hash(), "Invalid parent hash",);
 
-	// Uncompress
-	let mut db = MemoryDB::default();
-	let root = match sp_trie::decode_compact::<sp_trie::LayoutV1<HashFor<B>>, _, _>(
-		&mut db,
-		storage_proof.iter_compact_encoded_nodes(),
-		Some(parent_head.state_root()),
-	) {
-		Ok(root) => root,
+	// Create the db
+	let (db, root) = match storage_proof.to_memory_db(Some(parent_head.state_root())) {
+		Ok((db, root)) => (db, root),
 		Err(_) => panic!("Compact proof decoding failure."),
 	};
+
 	sp_std::mem::drop(storage_proof);
 
-	let backend = sp_state_machine::TrieBackend::new(db, root);
+	let backend = sp_state_machine::TrieBackend::new(db, *parent_head.state_root());
 
 	let _guard = (
 		// Replace storage calls with our own implementations