It was an obscure dev command, as it never worked reliably.
It would be much easier to re-implement once this is done.
This turned out to reveal a tiny leak on
tests/test_gossip.py::test_gossip_store_load_amount_truncated where we
didn't immedately free chan_ann if it was dangling.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>