[InstCombine][X86] Move simplifyX86FPMaxMin handling from simplifyDemandedVectorEltsIntrinsic to instCombineIntrinsic (#175441)
My fault for missing this when reviewing #174806 - technically we might
benefit from demanded elts handling for these intrinsics some day, but
the base implementation should be in instCombineIntrinsic
Noticed while reviewing #175375 which I recommended reuses more of the
simplifyX86FPMaxMin handling.