multi: rename ChannelAnnouncement to ChannelAnnouncment1

In preparation for adding the new ChannelAnnouncement2 message along
with a ChannelAnnouncement interface, we rename the existing message to
ChannelAnnouncement1.

funding/manager_test.go

@@ -1208,7 +1208,7 @@ func assertChannelAnnouncements(t *testing.T, alice, bob *testNode,
 		gotChannelUpdate := false
 		for _, msg := range announcements {
 			switch m := msg.(type) {
-			case *lnwire.ChannelAnnouncement:
+			case *lnwire.ChannelAnnouncement1:
 				gotChannelAnnouncement = true
 			case *lnwire.ChannelUpdate: