[clang] [clang-format] Remove YAML hack to emit a BasedOnStyle comment (PR #89228)

[Jannik Silvanus via cfe-commits]

jasilvanus wrote:

I've removed the dummy field and the comment now. This should prevent confusion.
I don't know whether anyone actually uses the emitted comment, there is no explanation,
and tests pass without it.

I suggest that if we later learn that there are valid uses that require the comment, we should add proper comment
support in the YAML writer, and add a test for it.

https://github.com/llvm/llvm-project/pull/89228