[clang] [NFC] Delete unused clang-formatted-files.txt file (PR #109220)

[Rahul Joshi via cfe-commits]

jurahul wrote:

@AaronBallman WDTY? The motivation of the change is that I see most of the changes in this file are a result of folks adding or deleting files, so its one less thing to take care of when doing so. Also the current list of files in this file is incomplete, further proving that this file is not used in any meaningful way. For example, "llvm/utils/TableGen/Basic/*" and "llvm/utils/TableGen/Common/*" are missing. I suspect there may be others as well.

https://github.com/llvm/llvm-project/pull/109220