Filming “The Revenant” in the freezing cold of Alberta nearly did him in, but Alejandro González Iñárritu isn’t complaining. “That’s our job,” says the director. His last film, “Birdman,” won big at last year’s Oscars, and “The Revenant” is up for 12 Academy Awards – more than any other film this year. Iñárritu downplays the controversy over the harsh shooting conditions, which prompted one crew member to call the film a “living hell.” In this extended conversation with Kurt Andersen, Iñárritu explains why he’s driven to extreme challenges – and why filming trees terrifies him.