[llvm] Revert "LangRef: Clarify llvm.minnum and llvm.maxnum about sNaN and signed zero (#112852)" (PR #168838)

[Ralf Jung via llvm-commits]

RalfJung wrote:

@phoebewang IIUC this fixes both https://github.com/llvm/llvm-project/issues/138303 and https://github.com/llvm/llvm-project/issues/169122; that could be added to the PR description.

https://github.com/llvm/llvm-project/pull/168838