Revert "[SimplifyCFG] Transform for redirecting phis between unmergeable BB and SuccBB (#67275)"

This reverts commit fc86d031.

This change breaks LLVM buildbot clang-aarch64-sve-vls-2stage
https://lab.llvm.org/buildbot/#/builders/176/builds/5474
I am going to revert this patch as the bot has been failing for more than a day without a fix.