Change the andesite pockets in the grimstone layers to normal stone pockets

In the 21w07a snapshot, pockets of andesite will still generate below y=0 where grimstone starts generating while granite and diorite will not. I think these pockets should be changed to stone pockets as I feel that it would make more sense to have some areas of a softer material than some areas of of one of the three extra stone types. This also makes andesite much more common than granite and diorite, which I am not a fan of. I feel that they should make them all generate equally across the underground, because they are all equally as useful.