ZHANGJIAKOU, China—This really is it for Shaun White. The three-time gold medalist made it clear that not only will the Beijing Games be his last Olympics, they’ll mark his final contest, too. During a reflective, sometimes emotional news conference Saturday, not far from the halfpipe where he’ll take his last competitive ride, the 35-year-old said that, yes, he’ll be hanging ’em up for good after the medal round next week. “In my mind, I’ve decided this will be my last competition,” he said. It’s a decision that’s been building since a soul-sucking training stop in Austria in November. He was dealing with nagging remnants from injuries to his knee … and back … and ankle. He got lost on the mountain with the sun going down. It was one of those rare times when snowboarding didn’t feel fun anymore. “A sad and surreal moment,” he called it. “But joyous, as …