We never call `listconfigs` in our tests with `experimental-offers` enabled,
so we didn't notice that the schema is wrong: it does not expect the
"plugin" field in 'fetchinvoice-noconnect'.
The next patch folds the fetchinvoice plugin into the offers plugin,
which is enabled even if `experimental-offers` isn't (for `decode`),
so we notice it.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
7f71e6353a