f Remove final hop validation from forwarding trampoline hops

The original version of this PR uses our final node validation to add
validation for forwarding node (this is not in the specification), and
has a TODO which notes that this should be replaced with a forwarding
error when we add more forwarding code.

This commit removes the temporary code (since we reject trampoline
forwards anyway), leaving addition of forwarding validation for later
work.

Author: carlaKC

lightning/src/ln/onion_payment.rs

@@ -161,9 +161,7 @@ pub(super) fn create_fwd_pending_htlc_info(
 				reason: LocalHTLCFailureReason::InvalidOnionPayload,
 				err_data: Vec::new(),
 			}),
-		onion_utils::Hop::TrampolineForward { ref outer_hop_data, next_trampoline_hop_data, next_trampoline_hop_hmac, new_trampoline_packet_bytes, trampoline_shared_secret, .. } => {
-			// TODO: return reason as forward issue, not as receiving issue when forwarding is ready.
-			check_trampoline_onion_constraints(outer_hop_data, next_trampoline_hop_data.outgoing_cltv_value, next_trampoline_hop_data.amt_to_forward)?;
+		onion_utils::Hop::TrampolineForward { next_trampoline_hop_data, next_trampoline_hop_hmac, new_trampoline_packet_bytes, trampoline_shared_secret, .. } => {
 			(
 				RoutingInfo::Trampoline {
 					next_trampoline: next_trampoline_hop_data.next_trampoline,
@@ -178,7 +176,7 @@ pub(super) fn create_fwd_pending_htlc_info(
 				None
 			)
 		},
-		onion_utils::Hop::TrampolineBlindedForward { ref outer_hop_data, next_trampoline_hop_data, next_trampoline_hop_hmac, new_trampoline_packet_bytes, trampoline_shared_secret, .. } => {
+		onion_utils::Hop::TrampolineBlindedForward { outer_hop_data, next_trampoline_hop_data, next_trampoline_hop_hmac, new_trampoline_packet_bytes, trampoline_shared_secret, .. } => {
 			let (amt_to_forward, outgoing_cltv_value) = check_blinded_forward(
 				msg.amount_msat, msg.cltv_expiry, &next_trampoline_hop_data.payment_relay, &next_trampoline_hop_data.payment_constraints, &next_trampoline_hop_data.features
 			).map_err(|()| {
@@ -190,13 +188,6 @@ pub(super) fn create_fwd_pending_htlc_info(
 					err_data: vec![0; 32],
 				}
 			})?;
-			check_trampoline_onion_constraints(outer_hop_data, outgoing_cltv_value, amt_to_forward).map_err(|e| {
-				InboundHTLCErr {
-					reason: LocalHTLCFailureReason::InvalidOnionBlinding,
-					err_data: vec![0; 32],
-					msg: e.msg,
-				}
-			})?;
 			(
 				RoutingInfo::Trampoline {
 					next_trampoline: next_trampoline_hop_data.next_trampoline,