Don't know that I've ever seen maggots on a black walnut before and I've picked up hundreds upon thousands of walnuts in my day....I think I would have remembered maggots.
We usually just left them lying around the yard until the hulls started to deteriorate a little so they could be easily stepped upon to crush the hull and remove the actual nut. Then the nuts were spread out somewhere dry to let them dry out more and let any juices/hull fibers dry and become more easily removed. After thoroughly dried they were stored in buckets until we could crack them.
I don't know of any nifty tricks to remove those hulls...we always just stepped on them, which popped them open and revealed the nut. I'm sure there are all kinds of machinery and such out there now that could help with hull removal. Some folks put them in the driveway and just run over them for awhile to remove the hulls.