Film fans often debate the necessity of a prequel film or TV series. Often, prequels serve only to shine a light on mysteries that should have remained in the dark. Those answers to questions you might have had about a character are rarely more interesting than the mystery about what makes someone tick. Ryan Murphy hopes that film fans will give his new prequel series, “Ratched,” a chance, even though it would appear from the newest trailer that the Netflix series is going to give audiences a lot of answers about an iconic character that we maybe didn’t need.