VIA insidemovies.ew.com When Quentin Tarantino’s western revenge-fantasy Django Unchained was first announced, casting rumors pegged Will Smith as the titular slave-turned-vigilante. But Smith, who teams with his son Jaden in this summer’s sci-fi epic After Earth, tells EW that he turned down the part because his character would’ve been second fiddle to the bounty hunter (played by Christoph Waltz) who teaches Django his trade . “Django wasn’t the lead, so it was like, I need to be the lead. The other character was the lead!” says the Men in Black star, whose departure opened the door for Jamie Foxx to play the role. Smith says that before he left the…