PARIS — Coco Gauff’s French Open title defense ended Saturday, on the court where she collapsed to the clay a year ago as the winner of a second Grand Slam title, a capacity crowd exploding for her, the biggest star in the sport triumphing on one of its biggest stages once again. Fifty-one weeks later the scenes on Court Philippe-Chatrier could not have been more different as Anastasia Potapova, the Russian-turned-Austrian who has blasted her way back to relevance this spring came back from a se