multi: rename AnnounceSignatures to AnnounceSignatures1

In preparation for adding a new message, AnnounceSignatures2 along with
an AnnounceSignatures interface, we rename the existing message to
AnnounceSignatures1.

peer/brontide.go

@@ -1966,7 +1966,7 @@ out:
 		case *lnwire.ChannelUpdate,
 			*lnwire.ChannelAnnouncement,
 			*lnwire.NodeAnnouncement,
-			*lnwire.AnnounceSignatures,
+			*lnwire.AnnounceSignatures1,
 			*lnwire.GossipTimestampRange,
 			*lnwire.QueryShortChanIDs,
 			*lnwire.QueryChannelRange,
@@ -2225,7 +2225,7 @@ func messageSummary(msg lnwire.Message) string {
 	case *lnwire.Error:
 		return fmt.Sprintf("%v", msg.Error())
 
-	case *lnwire.AnnounceSignatures:
+	case *lnwire.AnnounceSignatures1:
 		return fmt.Sprintf("chan_id=%v, short_chan_id=%v", msg.ChannelID,
 			msg.ShortChannelID.ToUint64())