LLParser: Simplify ParseInstructionMetadata(), NFC

Remove unused `PFS` variable and take the `Instruction` by reference.
(Not really related to PR23340, but might as well clean this up while
I'm here.)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235782 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed