Use _CustomJSONCodable as the sole signal for WKTs.
Use _CustomJSONCodable as the sole signal for WKTs.

Most of the code used _CustomJSONCodable as the signal, but this one spot was using
type lookup instead; this puts all the code on a consistent approach.

allevato/swift-protobuf,apple/swift-protobuf,apple/swift-protobuf,tbkka/swift-protobuf,cburrows/swift-protobuf,cburrows/swift-protobuf,allevato/swift-protobuf,apple/swift-protobuf,thomasvl/swift-protobuf,tbkka/swift-protobuf,allevato/swift-protobuf,thomasvl/swift-protobuf,thomasvl/swift-protobuf,apple/swift-protobuf,tbkka/swift-protobuf,tbkka/swift-protobuf,cburrows/swift-protobuf,thomasvl/swift-protobuf,allevato/swift-protobuf,allevato/swift-protobuf,cburrows/swift-protobuf,apple/swift-protobuf,tbkka/swift-protobuf,thomasvl/swift-protobuf,tbkka/swift-protobuf,cburrows/swift-protobuf,apple/swift-protobuf,allevato/swift-protobuf,tbkka/swift-protobuf,allevato/swift-protobuf,cburrows/swift-protobuf,apple/swift-protobuf,cburrows/swift-protobuf,thomasvl/swift-protobuf,thomasvl/swift-protobuf