[llvm] [VPlan] Remove original loop if dead after vectorization. (PR #155497)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> Btw, I'm not sure if you're aware, but we recently got an --update-tests option in lit which I've personally found invaluable: when this patch conflicts, you can update it in an instant.

Thanks for the heads-up! I was using my own script until now, but lit integration is more convenient.

https://github.com/llvm/llvm-project/pull/155497