gossipd: make sure we correctly move node announcement when *no* channel preceeds it in the gossip store.

We had the test backwards, so we moved it *all the time*.  This bloats our gossip store, as well as
not moving it in the case where we need to.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: gossipd: we would occasionally not show a node announcement in listnodes().

tests/test_gossip.py

@@ -2372,7 +2372,6 @@ def test_incoming_unreasonable(node_factory):
     l3.rpc.listincoming()
 
 
-@pytest.mark.xfail(strict=True)
 def test_gossmap_lost_node(node_factory, bitcoind):
     l1, l2, l3, l4 = node_factory.line_graph(4, wait_for_announce=True)