Setting html_root_url is still immensely useful when building crate documentation locally. If building with cargo doc --no-deps types are not linked unless the source crate specifies html_root_url.
Possible solutions like -Zrustdoc-map are still unstable. Until then, keeping the attribute still is useful and crates like version-sync ensures that all version numbers are kept in sync. After all, there might be more places with version duplication.