[llvm] [VPlan] Only store RecurKind + FastMathFlags in VPReductionRecipe. NFCI (PR #131300)

[Florian Hahn via llvm-commits]

fhahn wrote:

There's a new use of the recurrence descriptor added in https://github.com/llvm/llvm-project/pull/113903 by @ElvisWang123 . Would be good to check if RecurrenceKind is enough for that patch as well

https://github.com/llvm/llvm-project/pull/131300