[clang] [clang] Delete duplicate code in sourcemanager (PR #166236)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for this, but it's not yet clear to me that this is an NFC kind of change; can you explain why this logic is now duplicated in a bit more detail?

https://github.com/llvm/llvm-project/pull/166236