Getty Images Dallas Cowboys quarterback Dak Prescott was a full participant at OTAs. Dak Prescott’s return from hamstring surgery is ahead of schedule, and the Dallas Cowboys quarterback sounds like he has something to prove. Prescott participated fully during Tuesday’s OTAs and has been cleared for everything but contact. He was limited to just eight games last season after a hamstring avulsion that required surgery . Cowboys owner Jerry Jones had created some uncertainty earlier in the