The last day of the last Checker cab in New York should have been full of nostalgia and romance, the storied retirement of a much-loved machine integral to the city's lore and lure. Instead, it was filled with hassles. First there was the gnawing pain in Earl Johnson's left knee, a twinge of gout that made it wrenching for him to fold his 6-foot-1-inch frame into the driver's seat of the 1978 classic, and even more agonizing to get out. Then there was the awkward moment when