By John Cross You really have never seen anything like it. It was Arsenal’s biggest-ever away win in the Premier League, West Ham fans had left in their thousands by half time and surely even the celebration police would forgive the visitors enjoying this one. Bukayo Saka got a brilliant double and exorcised some ghosts of last season, and Declan Rice then got the best goal of the lot and did not celebrate out of respect for his old club. Rice need not have worried. By the time Rice got Arsenal’s sixth goal, most of the West Ham fans had left anyway. They departed in their thousands even by ha…