[testnet] Align testnet system parachain runtimes using RelayTreasuryLocation and SystemParachains in the same way (#2023)

This PR addresses several issues:
- simplify referencing `RelayTreasuryLocation` without needing
additional `RelayTreasury` struct
- fix for referencing `SystemParachains` from parachain with `parents:
1` instead of `parents: 0`
- removed hard-coded constants and fix tests for `asset-hub-rococo`
which was merged to master after
https://github.com/paritytech/polkadot-sdk/pull/1726

---------

Co-authored-by: command-bot <>

cumulus/parachains/runtimes/assets/asset-hub-rococo/src/lib.rs

@@ -1381,7 +1381,13 @@ impl_runtime_apis! {
 					MultiAsset { fun: Fungible(UNITS), id: Concrete(TokenLocation::get()) },
 				));
 				pub const CheckedAccount: Option<(AccountId, xcm_builder::MintLocation)> = None;
-				pub const TrustedReserve: Option<(MultiLocation, MultiAsset)> = None;
+				// AssetHubRococo trusts AssetHubWococo as reserve for WOCs
+				pub TrustedReserve: Option<(MultiLocation, MultiAsset)> = Some(
+					(
+						xcm_config::bridging::to_wococo::AssetHubWococo::get(),
+						MultiAsset::from((xcm_config::bridging::to_wococo::WocLocation::get(), 1000000000000 as u128))
+					)
+				);
 			}
 
 			impl pallet_xcm_benchmarks::fungible::Config for Runtime {