“I’m the champ, I’ll just leave it at that.” For five years in the UFC, Demetrious Johnson was the undisputed king at 125 pounds. But after losing the title in 2018 to Henry Cejudo, “Mighty Mouse” left for Singapore and signed with ONE Championship where he is the current champion at flyweight after exacting revenge on Adriano Moraes over the weekend via a fourth-round flying knee KO win. But unlike in the UFC, ONE’s flyweight division is contested at 135 pounds, a weight that Johnson is more comfortable at. And as he told Ariel Helwani in a recent appearance on…