[llvm] [VPlan] Remove loop region in optimizeForVFAndUF. (PR #108378)

[Florian Hahn via llvm-commits]

fhahn wrote:

After merging initial skeleton creation, we cannot easily get the vector preheader any longer without the region. Putting this on hold for a bit.

https://github.com/llvm/llvm-project/pull/108378