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.

discovery/gossiper.go

@@ -1416,7 +1416,7 @@ func (d *AuthenticatedGossiper) networkHandler() {
 			switch announcement.msg.(type) {
 			// Channel announcement signatures are amongst the only
 			// messages that we'll process serially.
-			case *lnwire.AnnounceSignatures:
+			case *lnwire.AnnounceSignatures1:
 				emittedAnnouncements, _ := d.processNetworkAnnouncement(
 					announcement,
 				)
@@ -2041,7 +2041,7 @@ func (d *AuthenticatedGossiper) processNetworkAnnouncement(
 	// A new signature announcement has been received. This indicates
 	// willingness of nodes involved in the funding of a channel to
 	// announce this new channel to the rest of the world.
-	case *lnwire.AnnounceSignatures:
+	case *lnwire.AnnounceSignatures1:
 		return d.handleAnnSig(nMsg, msg)
 
 	default:
@@ -2129,7 +2129,7 @@ func (d *AuthenticatedGossiper) fetchNodeAnn(
 // MessageStore is seen as stale by the current graph.
 func (d *AuthenticatedGossiper) isMsgStale(msg lnwire.Message) bool {
 	switch msg := msg.(type) {
-	case *lnwire.AnnounceSignatures:
+	case *lnwire.AnnounceSignatures1:
 		chanInfo, _, _, err := d.cfg.Graph.GetChannelByID(
 			msg.ShortChannelID,
 		)
@@ -3200,7 +3200,7 @@ func (d *AuthenticatedGossiper) handleChanUpdate(nMsg *networkMsg,
 
 // handleAnnSig processes a new announcement signatures message.
 func (d *AuthenticatedGossiper) handleAnnSig(nMsg *networkMsg,
-	ann *lnwire.AnnounceSignatures) ([]networkMsg, bool) {
+	ann *lnwire.AnnounceSignatures1) ([]networkMsg, bool) {
 
 	needBlockHeight := ann.ShortChannelID.BlockHeight +
 		d.cfg.ProofMatureDelta