Marvin Bracy gave away nearly three years of his track career in a failed attempt to make the NFL as a wide receiver. But the former Boone High School football/track speedster never stopped believing he could be one of the fastest men in the world. He proved to be just that on Saturday with a silver medal performance in the 100-meter dash at the world championships of track and field in Eugene, Oregon. Bracy, 28, nearly struck gold. The 2016 Olympian clocked a 9.88-second time to finish second, two-hundredths of a second behind champion Fred Kerley (9.86). “I thought I won. Fred is a helluva f…