Director Danny Boyle’s “Yesterday” suggests a number of Beatles titles. “You Can’t Do That.” “Run for Your Life.” And, mostly, “Help!” Any movie that champions the Beatles is on the righteously right track. (“Anyone who is against the Beatles is against life,” a character in a now-forgotten film once muttered, memorably.) The story is based on such an audacious idea it should almost be granted immunity from prosecution. But how did such a crazy premise—a world in which the Beatles basically have never existed—turn into such a routine romantic comedy?