[llvm] Revert "LangRef: Clarify llvm.minnum and llvm.maxnum about sNaN and signed zero (#112852)" (PR #138451)

[Ralf Jung via llvm-commits]

RalfJung wrote:

This is absolutely required to fix https://github.com/llvm/llvm-project/issues/169122. One can't just change the LangRef if the new text contradicts existing practice in backends (and optimizations, see https://github.com/llvm/llvm-project/issues/138303).

https://github.com/llvm/llvm-project/pull/138451