The world’s greatest assassin is about to retire when his former boss decides he’s a liability. Hoping for a silly shoot ‘em up like The Mechanic or John Wick? Sorry to disappoint but Polar, released this week by Netflix, isn’t it. Instead, this is a film so terrible that it’s an early contender for the year-end worst of lists. Duncan Vizla (Mads Mikkelsen) is the great assassin preparing for his 50th birthday and mandatory retirement. He’s already started to wind down by moving to a snow covered one-street town in Montana. There, Duncan wanders around his log cabin, buys a…