[llvm] Revert "[SimplifyCFG] Deduce paths unreachable if they cause div/rem UB" (PR #137741)

[Bill Wendling via llvm-commits]

bwendling wrote:

> The kernel has a lot of highly dubious, incredibly fragile analysis tooling, which keeps producing false positives every time optimization behavior shifts in the most minuscule ways. I am very much not willing to revert correct changes to satisfy it.
> 
> I might have accepted a temporary revert if this change had landed a few days ago, but we're long past that.

But this isn't a false positive. It really does lead to genuine bad code. And why would a few days make such a difference here?

https://github.com/llvm/llvm-project/pull/137741