AsmParser: Use normal references for metadata attachments, NFC

Remove special parsing logic for metadata attachments.  Now that
`DebugLoc` is stored normally (since the metadata/value split), we don't
need this special forward referencing logic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225698 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed