By Sarah N. Lynch WASHINGTON (Reuters) – GNC Holdings Inc, the largest global dietary supplement retailer, has agreed to pay $2.25 million to avoid federal prosecution over its alleged sale of illegal dietary supplements, the U.S. Department of Justice said on Wednesday. GNC admitted no wrongdoing as part of the agreement. The non-prosecution agreement, under which GNC will reform some practices, stems from allegations that it sold a misbranded supplement in 2013 called OxyElite Pro Advanced Formula, made by Dallas-based USP Labs.