[clang] Revert "[clang][docs] Generate command line reference as Markdown" (PR #221937)

[Shunsuke Watanabe via cfe-commits]

https://github.com/s-watanabe314 approved this pull request.

I was just looking into the cause of the build failure. Thanks for letting me know.

https://github.com/llvm/llvm-project/pull/221937