[llvm] [NFC] Eliminate needs of Emacs tag and file name in file headers (PR #118553)

[Rahul Joshi via llvm-commits]

jurahul wrote:

@nikic and @AaronBallman PTAL at the discourse thread above and see if we want to make this amendment to the coding standards. This does not mean that all files will be immediately updated to strip out the current header, but over time.

https://github.com/llvm/llvm-project/pull/118553