remove repetitive words

Signed-off-by: cuinix <915115094@qq.com>

htlcswitch/switch.go

@@ -1469,7 +1469,7 @@ func (s *Switch) failAddPacket(packet *htlcPacket, failure *LinkError) error {
 
 	log.Error(failure.Error())
 
-	// Create a failure packet for this htlc. The the full set of
+	// Create a failure packet for this htlc. The full set of
 	// information about the htlc failure is included so that they can
 	// be included in link failure notifications.
 	failPkt := &htlcPacket{