Turbopack: Remove dead generic_type_macro code (#88455)
I deleted the code that used this a long time ago in https://github.com/vercel/next.js/pull/70817
The rational for why I deleted the uses of this code is here (generics in turbo-tasks would be nice, but this implementation was too limited to be worth the complexity): https://github.com/vercel/turborepo/pull/8843#issuecomment-2253158412
