IR: MDNode => Value: Instruction::getAllMetadataOtherThanDebugLoc()

Change `Instruction::getAllMetadataOtherThanDebugLoc()` from a vector of
`MDNode` to one of `Value`.  Part of PR21433.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221167 91177308-0d34-0410-b5e6-96231b3b80d8