Rename Instruction::dropUnknownMetadata() to dropUnknownNonDebugMetadata()
and make it always preserve debug locations, since all callers wanted this
behavior anyway.

This is addressing a post-commit review feedback for r245589.

NFC (inside the LLVM tree).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245622 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed