[llvm] [LoopVectorize][NFC] Fix arith-fp-frem-costs.ll test to use new vplan cost model (PR #120742)

[Paschalis Mpeis via llvm-commits]

https://github.com/paschalis-mpeis approved this pull request.

LGTM. Thanks for moving the tests to the new cost model.

https://github.com/llvm/llvm-project/pull/120742