DRY the comparison blocks in update_claims_view_from_matched_txn

In `update_claims_view_from_matched_txn` we have two different
tx-equivalence checks which do the same thing - both check that the
tx which appeared on chain spent all of the outpoints which we
intended to spend in a given package. While one is more effecient
than the other (but only usable in a subset of cases), the
difference between O(N) and O(N^2) when N is 1-5 is trivial.

While it is possible we hit this code with just shy of 900 HTLC
outputs in a channel, we're still talking about only ~400k
inner iterations, and only in response to an on-chain transaction
which spends some inputs out from under us. Further, if we're
actually worried about the time complexity here (which we shouldn't
be), we can't just have one slow version and another that's fine -
we'd still need to worry about the slow version.

Here we simply drop the faster version, leaving the full-comparison
version in place and using it always.

Author: TheBlueMatt

lightning/src/chain/onchaintx.rs

@@ -733,31 +733,14 @@ impl<ChannelSigner: Sign> OnchainTxHandler<ChannelSigner> {
 						// outpoints to know if transaction is the original claim or a bumped one issued
 						// by us.
 						let mut are_sets_equal = true;
-						if !request.requires_external_funding() || !request.is_malleable() {
-							// If the claim does not require external funds to be allocated through
-							// additional inputs we can simply check the inputs in order as they
-							// cannot change under us.
-							if request.outpoints().len() != tx.input.len() {
+						// Do a linear search for each input (we don't expect large input sets to
+						// exist) to ensure the request's input set is fully spent to be resilient
+						// against the external claim reordering inputs.
+						for request_input in request.outpoints() {
+							if tx.input.iter().find(|input| input.previous_output == *request_input).is_none() {
 								are_sets_equal = false;
-							} else {
-								for (claim_inp, tx_inp) in request.outpoints().iter().zip(tx.input.iter()) {
-									if **claim_inp != tx_inp.previous_output {
-										are_sets_equal = false;
-									}
-								}
-							}
-						} else {
-							// Otherwise, we'll do a linear search for each input (we don't expect
-							// large input sets to exist) to ensure the request's input set is fully
-							// spent to be resilient against the external claim reordering inputs.
-							let mut spends_all_inputs = true;
-							for request_input in request.outpoints() {
-								if tx.input.iter().find(|input| input.previous_output == *request_input).is_none() {
-									spends_all_inputs = false;
-									break;
-								}
+								break;
 							}
-							are_sets_equal = spends_all_inputs;
 						}
 
 						macro_rules! clean_claim_request_after_safety_delay {