Remove the unused maximum and minimum functions in vec256_base (#56313)
Summary:
They are unused, unrelated to vectorization, and confusing for code
readers (each of them have 2 overloads that are actually used).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56313
Reviewed By: bdhirsh
Differential Revision: D27854290
Pulled By: ezyang
fbshipit-source-id: 14945ceac39a3f19e5d0f8d762b17f8c2172b966
