Dr. Mehmet Oz is fast becoming a taxpayer’s dream at the helm of the Centers for Medicare and Medicaid Services. Fighting “waste, fraud, and abuse” isn’t just a tired slogan to him — it’s a mandate. And he’s enforcing it. He arrived with a reputation as the new sheriff in town: Few physicians would want to take on the task of digging through a toxic pile of fraud, where scammers long enjoyed siphoning billions from taxpayers. His mandate was straightforward: Visit the nation’s worst hotspots —