[llvm] [UnrollAndJam] Do not preserve loop nests if a loop was fully unrolled. (PR #133510)

[Arthur Eubanks via llvm-commits]

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

if the `PA.preserve<LoopNestAnalysis>();` is correct in cases where we don't remove the loop, then lgtm

https://github.com/llvm/llvm-project/pull/133510