gossipd: don't discard node_announcements with old timestamps.

It really, really doesn't matter.  But we were dramatically reducing
our view of the network:

In my gossip_store (mainnet):
  channel_announcement: 30349
  channel_update: 55119
  node_announcment: 1783

Changelog-Fixed: No longer discard most node_announcements (fixes #3194)
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

gossipd/routing.c

@@ -2414,14 +2414,6 @@ bool routing_add_node_announcement(struct routing_state *rstate,
 		status_debug("Received node_announcement for node %s",
 			     type_to_string(tmpctx, struct node_id, &node_id));
 
-	/* Check timestamp is sane (unless from gossip_store). */
-	if (!index && !timestamp_reasonable(rstate, timestamp)) {
-		status_debug("Ignoring node_announcement timestamp %u for %s",
-			     timestamp,
-			     type_to_string(tmpctx, struct node_id, &node_id));
-		return false;
-	}
-
 	node = get_node(rstate, &node_id);
 
 	if (node == NULL || !node_has_broadcastable_channels(node)) {