[llvm] [SCEV] Avoid erase+insert in constant folding (PR #101642)

[Philip Reames via llvm-commits]

https://github.com/preames commented:

As much as this was my suggestion, I'm not sure this is worth the resulting complexity.  I left comments, but if you want to just abandon this, I'm fine with that too.  

https://github.com/llvm/llvm-project/pull/101642