[InstCombine] Remove nnan requirement for transformation to fabs from select

In this patch, the "nnan" requirement is removed for the canonicalization of select with fcmp to fabs.
(i) FSub logic: Remove check for nnan flag presence in fsub. Example: https://alive2.llvm.org/ce/z/751svg (fsub).
(ii) FNeg logic: Remove check for the presence of nnan and nsz flag in fneg. Example: https://alive2.llvm.org/ce/z/a_fsdp (fneg).

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D106872