GENEVA/DUBAI, July 8 (Reuters) – Iran threatened on Monday to restart deactivated centrifuges and ramp up its enrichment of uranium to 20 percent purity as its next potential big moves away from a 2015 nuclear agreement that Washington abandoned last year. The threats, made by the spokesman for Tehran’s nuclear agency, would go far beyond the small steps Iran has taken in the past week to nudge its stocks of fissile material just beyond limits in the nuclear pact.