Where to start, when this might be the end? Last week’s episode, “Babylon,” ended on a charming note, with the lovely notes of The Lumineers’ “Ho Hey.” But the season finale of The X-Files is bleak, like Stephen King’s The Stand bleak. Everyone’s got the superflu. We last see Scully and Mulder on a jam-packed bridge, cars parked haphazardly, drivers and passengers dying. It might be the end of the world; maybe it’s just the end of X-Files. Either way, it feels like tragedy. It’s the end, too, of a certain kind of television show.