This Sunday, “The X-Files” returns to Fox for a limited-engagement series of six episodes. David Duchovny and Gillian Anderson will reprise their roles as Fox Mulder and Dana Scully, parts that made them household names in the 1990s. At one point, it seemed like “The X-Files” was everywhere. Fans became obsessed with the show’s examination of alien encounters and government conspiracies. Another popular Fox show, “The Simpsons,” decided to parody the show early on, but it wasn’t an easy task. Here, “Simpsons” executive producer Al Jean, producer Mike Reiss, animator and consulting producer David Silverman, writer Reid...