Three episodes into Dexter: Original Sin, it’s clear the show has a good sense of humor about itself — this episode has a lot of talking-parrot moments — and also isn’t afraid to embrace the gruesomeness of the original series. But as we delve further into flashbacks involving Harry and his doomed informant, Laura Moser, it’s becoming less clear what story the show is trying to tell that we don’t already know. At least “Miami Vice” delivers...