[clang-tools-extra] [clang-doc] Remove unused simple_ilist comparison operators (NFC) (PR #206309)

[Paul Kirth via cfe-commits]

https://github.com/ilovepi approved this pull request.

LGTM if the bots are happy with this. Thanks for catching and fixing the issue. 

@evelez7 any progress on dropping YAML/legacy MD implementation? The legacy implementations are becoming problematic, as we're not really maintaining them appropriately. 

https://github.com/llvm/llvm-project/pull/206309