[llvm] [InstCombine] Revert the `signed icmp -> unsigned icmp` canonicalization when folding `icmp Pred min|max(X, Y), Z` (PR #76685)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> BTW, should we add a flag like nneg to indicate that an unsigned icmp can be treated as a signed one?

@nikic Any thoughts?

https://github.com/llvm/llvm-project/pull/76685