Revert "[ThinLTO] Serialize the Module SourceFileName to/from LLVM assembly"

This reverts commit r264869. I am seeing Windows bot failures due to the
"\" in the path being mishandled at some point (seems to be interpreted
wrongly at some point and llvm-as | llvm-dis is yielding some junk
characters). Need to investigate.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264871 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed