NEW YORK — Two familiar names were bounced from the US Open and one of them is done forever with singles. John Isner, the hard-serving American, retired from singles tennis after losing Thursday afternoon to Michael Mmoh on Grandstand, 3-6, 4-6, 7-6 (7), 6-4, 7-6 (10). It was, in some ways, a fitting ending for Isner — a 5-set tiebreak defined by aces and few breaks. But he also blew a golden…