LeBron James watched from the bench in street clothes. The show he saw wasn’t very pretty. “There’ll be no video on this game, hopefully,” Celtics coach Doc Rivers said. “It was not a piece of art.” Boston plodded to an 80-70 win over the Cleveland Cavaliers on Sunday. But the NBA’s leading scorer was sidelined with a sprained finger, the NBA’s best team had little energy, and the crowd that showed…