garden: fix broken treaty JSON
garden: fix broken treaty JSON

For some reason, a %uv case was added to the JSON serialiser for $case.
$case has no such case in the union, and so this does not make sense.

ngzax/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,urbit/urbit,urbit/urbit,ngzax/urbit