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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

I don't think this file is actually unused; it was committed with the original PR adding the script: 5aca8bb963a43b62f37305f7eb07476631ea9f2a (https://reviews.llvm.org/D111000 was the review)

I've added @mydeveloperday as a reviewer for confirmation though

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