discovery+graph: get inbound fee directly from ChannelUpdate

Remove the previously added TODOs which would extract InboundFee info
from the ExtraOpaqueData of a ChannelUpdate at the time of
ChannelEdgePolicy construction. These can now be replaced by using the
newly added InboundFee record on the ChannelUpdate message.

graph/builder.go

@@ -11,7 +11,6 @@ import (
 	"github.com/go-errors/errors"
 	"github.com/lightningnetwork/lnd/batch"
 	"github.com/lightningnetwork/lnd/chainntnfs"
-	"github.com/lightningnetwork/lnd/fn/v2"
 	graphdb "github.com/lightningnetwork/lnd/graph/db"
 	"github.com/lightningnetwork/lnd/graph/db/models"
 	"github.com/lightningnetwork/lnd/lnutils"
@@ -955,25 +954,10 @@ func (b *Builder) ApplyChannelUpdate(msg *lnwire.ChannelUpdate1) bool {
 		MaxHTLC:                   msg.HtlcMaximumMsat,
 		FeeBaseMSat:               lnwire.MilliSatoshi(msg.BaseFee),
 		FeeProportionalMillionths: lnwire.MilliSatoshi(msg.FeeRate),
+		InboundFee:                msg.InboundFee.ValOpt(),
 		ExtraOpaqueData:           msg.ExtraOpaqueData,
 	}
 
-	// Extract the inbound fee from the ExtraOpaqueData, if present.
-	//
-	// TODO(elle): this can be removed once we define the optional TLV
-	// field on the lnwire.ChannelUpdate itself.
-	var inboundFee lnwire.Fee
-	typeMap, err := update.ExtraOpaqueData.ExtractRecords(&inboundFee)
-	if err != nil {
-		log.Errorf("%v: %v", graphdb.ErrParsingExtraTLVBytes, err)
-		return false
-	}
-
-	val, ok := typeMap[lnwire.FeeRecordType]
-	if ok && val == nil {
-		update.InboundFee = fn.Some(inboundFee)
-	}
-
 	err = b.UpdateEdge(update)
 	if err != nil && !IsError(err, ErrIgnored, ErrOutdated) {
 		log.Errorf("Unable to apply channel update: %v", err)