During the endless final sequence of “Space Jam: A New Legacy,” Porky Pig calls himself “the Notorious P.I.G.” and begins to rap. “This pig is lit,” the Looney Tune says. “I’m super legit.” Porky should’ve added: “And my movie is s–t.” In the pantheon of misguided sequels and reboots, “A New Legacy” is right up there with “Paul Blart: Mall Cop 2” and “Little Fockers.” The original 1996 “Space Jam” wasn’t top-drawer either, but it made a buck at the box office. So, money-grubbing Warner Bros. took 25 years to crank out a follow-up that’s far, far worse. And they know it. Over its interminable, nearly two-hour runtime, the film repeatedly mocks its very existence. “I’m a ballplayer,” says star LeBron James, taking the reins from the original’s Michael Jordan, during a pitch meeting with WB execs. “And athletes acting — it never goes well.” That’s especially true of cardboard James. The villain of the movie is the WB algorithm, called, ugh, Al G. Rhythm (Don Cheadle), who is responsible for drumming up all of the studio’s soulless content, such as… this! When LeBron arrives in Tune World, where all the Looney Tunes are supposed to live, he finds it largely abandoned.