[llvm] Revert "[InstCombine] Teach foldSelectOpOp about samesign" (PR #124123)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon approved this pull request.

Since one other person (@goldsteinn) has verified, this should land without delay.

https://github.com/llvm/llvm-project/pull/124123