John Floyd was trimming the trees in his sister’s yard when he got the news just before Thanksgiving.More than 37 years after his arrest for a 1980 killing in the French Quarter, and months after a federal judge set him free, Orleans Parish District Attorney Leon Cannizzaro’s office was dropping its bid to put him on trial again. An unfavorable decision from the U.S. Supreme Court had proven too much for prosecutors.Floyd set aside his chainsaw and sat down.“It was shocking,” he said recently. “Made me feel so good.”Floyd, 69, was released from the Louisiana State Penitentiary at Angola last June, after a federal district judge tossed out his murder conviction in the slashing death of Times-Picayune proofreader William Hines.