grace period RPC fails with uninformative error when delegate is not registered
results in:
[{"kind":"permanent","id":"proto.003-PsddFKi3.context.storage_error","missing_key":["contracts","index","ed25519","3f","71","95","b0","02","fa74de55a3c7aac241d4a2a9791436","delegate_desactivation"],"function":"get"}]
It should probably either report that the contract is not a registered delegate, or report a grace period that has already expired.