Fix xcm config for coretime. (#3768)

Fixes https://github.com/paritytech/polkadot-sdk/issues/3762 .

---------

Co-authored-by: eskimor <eskimor@no-such-url.com>
Co-authored-by: Adrian Catangiu <adrian@parity.io>

polkadot/runtime/westend/src/xcm_config.rs

@@ -41,10 +41,11 @@ use xcm_builder::{
 	AccountId32Aliases, AllowExplicitUnpaidExecutionFrom, AllowKnownQueryResponses,
 	AllowSubscriptionsFrom, AllowTopLevelPaidExecutionFrom, ChildParachainAsNative,
 	ChildParachainConvertsVia, DescribeAllTerminal, DescribeFamily, FrameTransactionalProcessor,
-	FungibleAdapter, HashedDescription, IsConcrete, MintLocation, OriginToPluralityVoice,
-	SignedAccountId32AsNative, SignedToAccountId32, SovereignSignedViaLocation, TakeWeightCredit,
-	TrailingSetTopicAsId, UsingComponents, WeightInfoBounds, WithComputedOrigin, WithUniqueTopic,
-	XcmFeeManagerFromComponents, XcmFeeToAccount,
+	FungibleAdapter, HashedDescription, IsChildSystemParachain, IsConcrete, MintLocation,
+	OriginToPluralityVoice, SignedAccountId32AsNative, SignedToAccountId32,
+	SovereignSignedViaLocation, TakeWeightCredit, TrailingSetTopicAsId, UsingComponents,
+	WeightInfoBounds, WithComputedOrigin, WithUniqueTopic, XcmFeeManagerFromComponents,
+	XcmFeeToAccount,
 };
 use xcm_executor::XcmExecutor;
 
@@ -142,13 +143,12 @@ impl Contains<Location> for OnlyParachains {
 	}
 }
 
-pub struct CollectivesOrFellows;
-impl Contains<Location> for CollectivesOrFellows {
+pub struct Fellows;
+impl Contains<Location> for Fellows {
 	fn contains(location: &Location) -> bool {
 		matches!(
 			location.unpack(),
-			(0, [Parachain(COLLECTIVES_ID)]) |
-				(0, [Parachain(COLLECTIVES_ID), Plurality { id: BodyId::Technical, .. }])
+			(0, [Parachain(COLLECTIVES_ID), Plurality { id: BodyId::Technical, .. }])
 		)
 	}
 }
@@ -172,8 +172,8 @@ pub type Barrier = TrailingSetTopicAsId<(
 			AllowTopLevelPaidExecutionFrom<Everything>,
 			// Subscriptions for version tracking are OK.
 			AllowSubscriptionsFrom<OnlyParachains>,
-			// Collectives and Fellows plurality get free execution.
-			AllowExplicitUnpaidExecutionFrom<CollectivesOrFellows>,
+			// Messages from system parachains or the Fellows plurality need not pay for execution.
+			AllowExplicitUnpaidExecutionFrom<(IsChildSystemParachain<ParaId>, Fellows)>,
 		),
 		UniversalLocation,
 		ConstU32<8>,