LOS ANGELES (Reuters) – Arnold Schwarzenegger, talking about his affair with a family housekeeper for the first time in a television interview, said it was "the stupidest thing" he did in his marriage to Maria Shriver and said it "inflicted tremendous pain" on his family. In a "60 Minutes" interview with reporter Leslie Stahl due to air on September 30, Schwarzenegger admitted that he lied to Shriver about the affair. CBS released a clip of the interview on Friday. "I think it was the stupidest thing I've done in the whole relationship. It was terrible. …