I think they are pretty useless and make the docs harder to read.
Set the COLLABORATION_GRAPH, INCLUDE_GRAPH and INCLUDED_BY_GRAPH variables all to NO.
The changes are similar to the ones done in https://github.com/googleapis/google-cloud-cpp/pull/397, but I did not remove the class graph, I think that one is actually helpful.
Not sure who to add as reviewers (none of the codeowners files seem to mention a owner for docs...), so adding some frontend people.