[LV] Consolidate shouldOptimizeForSize and remove unused BFI/PSI. NFC#168697

lukel97 merged 3 commits intollvm:mainllvm/llvm-project:mainfrom

lukel97:loop-vectorize/consolidate-shouldOptForSizelukel97/llvm-project:loop-vectorize/consolidate-shouldOptForSizeCopy head branch name to clipboard