Revert "[EarlyIfConversion] Avoid producing selects with identical operands"

This reverts commit 3d27b5d2.

Broke one of the PPC tests, which I didn't see because I usually build with
only the x86/AARch64 targets enabled... oops.

https://lab.llvm.org/buildbot#builders/109/builds/13834

llvm/test/CodeGen/PowerPC/expand-foldable-isel.ll