Personally, I wouldn't worry about it. Chickens who are out on free range get a whole lot more calcium than is in that bag of layer, and you don't see them dropping dead from too much calcium. In fact, I'd venture to bet that aside from predation (and maybe not even then, b/c chickens in a run are not as able to escape from a predator that gets into their run) chickens who free range and have all that calcium from greens and insects in their diet live longer than chickens who only get layer feed.
