They may be talking about actually removing whole standards not just specifics of standards like this. FTP is close but it was always adjacent to web browsing. Perhaps HTTP 1.0 removal is closest, but is a different level of abstraction than XSLT which is potentially and subtly everywhere.
onunload: https://developer.chrome.com/docs/web-platform/deprecating-u...
Mutation events (replaced by MutationObserver): https://developer.chrome.com/blog/mutation-events-deprecatio...
FTP URLs: https://developer.chrome.com/blog/deps-rems-95#ftp_support_r...
Here's useful documentation on their process, which they sometimes call Chrome Variations and sometimes Origin Trials: https://developer.chrome.com/docs/web-platform/chrome-variat...