Do not include :code in the storage proof if not required (#480)

This is basically a hack that prevents the inclusion of `:code` in the
storage proof. A proper fix requires some changes to the trie crate to
not include nodes that aren't read.

test/service/src/chain_spec.rs

@@ -111,6 +111,7 @@ fn testnet_genesis(
 				.to_vec(),
 			..Default::default()
 		},
+		cumulus_pallet_parachain_system: Default::default(),
 		pallet_balances: cumulus_test_runtime::BalancesConfig {
 			balances: endowed_accounts
 				.iter()