We can actually delete it before counters are updated:
```
wait_for(lambda: len(l3.rpc.listinvoices()['invoices']) == 2)
> assert l3.rpc.autoclean_status()['autoclean']['expiredinvoices']['cleaned'] == 3
E assert 1 == 3
tests/test_plugin.py:3266: AssertionError
```
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>