lnwallet: inline processUpdateFee and remove the function entirely

In this commit we observe that the previous commit reduced the role
of this function to a single assignment statement with numerous newly
irrelevant parameters. This commit makes the choice of inlining it at
the two call-sites within evaluateHTLCView and removing the funciton
definition entirely. This also allows us to drop a huge portion of
newly irrelevant test code.

lnwallet/channel.go

@@ -2932,9 +2932,11 @@ func (lc *LightningChannel) evaluateHTLCView(view *HtlcView, ourBalance,
 			)
 
 			if h == 0 {
-				processFeeUpdate(
-					entry, &newView.FeePerKw, nextHeight,
-					whoseCommitChain,
+				// If the update wasn't already locked in,
+				// update the current fee rate to reflect this
+				// update.
+				newView.FeePerKw = chainfee.SatPerKWeight(
+					entry.Amount.ToSatoshis(),
 				)
 
 				if mutateState {
@@ -2996,11 +2998,14 @@ func (lc *LightningChannel) evaluateHTLCView(view *HtlcView, ourBalance,
 			)
 
 			if h == 0 {
-				processFeeUpdate(
-					entry, &newView.FeePerKw, nextHeight,
-					whoseCommitChain,
+				// If the update wasn't already locked in,
+				// update the current fee rate to reflect this
+				// update.
+				newView.FeePerKw = chainfee.SatPerKWeight(
+					entry.Amount.ToSatoshis(),
 				)
 
+
 				if mutateState {
 					entry.addCommitHeights.SetForParty(
 						whoseCommitChain, nextHeight,
@@ -3206,17 +3211,6 @@ func processRemoveEntry(htlc *paymentDescriptor, ourBalance,
 	}
 }
 
-// processFeeUpdate processes a log update that updates the current commitment
-// fee.
-func processFeeUpdate(feeUpdate *paymentDescriptor,
-	feeRef *chainfee.SatPerKWeight, nextHeight uint64,
-	whoseCommitChain lntypes.ChannelParty) {
-
-	// If the update wasn't already locked in, update the current fee rate
-	// to reflect this update.
-	*feeRef = chainfee.SatPerKWeight(feeUpdate.Amount.ToSatoshis())
-}
-
 // generateRemoteHtlcSigJobs generates a series of HTLC signature jobs for the
 // sig pool, along with a channel that if closed, will cancel any jobs after
 // they have been submitted to the sigPool. This method is to be used when