“Mufasa: The Lion King” has one very important thing going for it: an original story. That may seem like faint praise or at least a very, very low bar in the grand scheme of things. But in a landscape where Disney continues to remake its animated catalogue in slightly different, and usually less interesting, forms whether “live action” or “photorealistic” that usually only serves to remind how good the 2D animation was, originality is not to be undervalued.