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

[Rahul Joshi via cfe-commits]

jurahul wrote:

@AaronBallman ping to comment on this again. Not only does this have files missing, it also includes file names that do not exist anymore in the repo:

```
clang/docs/tools/clang-formatted-files.txt:llvm/include/llvm/DWP/DWPStringPool.h
clang/docs/tools/clang-formatted-files.txt:llvm/lib/CodeGen/AsmPrinter/DwarfStringPool.h
clang/docs/tools/clang-formatted-files.txt:llvm/lib/Target/NVPTX/ManagedStringPool.h
```

So, I think it's best to cleanup and delete the file.

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