The chain has made carrying the peanuts optional for franchisees and it looks like a number of them have opted out.
If you take a look at the McDonald's website, the image for all three sundaes (Caramel, Strawberry, and Hot Fudge) no longer includes a sprinkling of nuts on top and nuts are no longer listed among the sundaes' ingredients.
Depending on pricing (which varies with location), if the difference between a sundae and a vanila cone is just sauce, it makes buying the cheaper cone much more attractive.
Photo via McDonald's.