{Firrtl, Circuit}Option should be Unserializable (#1278)

FirrtlOption and CircuitOption represent, respectively, something that
is convertible to FirrtlOptions or something that is convertible to a
FirrtlCircuitAnnotation. Neither of these is intended to be serialized
automatically in output JSON.

This has the effect of *not* JSON-serializing the
FirrtlCircuitAnnotation. This serialization is supposed to be to a
file via an emitter.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>