Mercedes-AMG and the C-Class, a symbiosis that has given us one of the finest compact luxury coupes around year after year, is rumored to completely reinvent itself with a 2021 model that will ditch V8 power in favor of something more polar bear friendly. For now, the C63 continues to battle its biggest rival, the BMW M4, with its V8 heart intact. Rear-wheel-drive and a nine-speed automatic gearbox are the order of the day, with propulsion coming from…