server: remove peer from SyncManager on VerAckReceived

Peers are now added to the SyncManager if we receive their verack, but
we'd still attempt to remove them from the SyncManager if we didn't
receive it.

server.go

@@ -2058,7 +2058,7 @@ func (s *server) peerDoneHandler(sp *serverPeer) {
 	s.donePeers <- sp
 
 	// Only tell sync manager we are gone if we ever told it we existed.
-	if sp.VersionKnown() {
+	if sp.VerAckReceived() {
 		s.syncManager.DonePeer(sp.Peer)
 
 		// Evict any remaining orphans that were sent by the peer.