Currently, on all responses mw.config includes configuration variables wgCookiePrefix, wgCookieDomain, wgCookiePath, and wgCookieExpiration. These are documented as being
@internal For mediawiki.cookie
However, since rMWa0370fe3c958: mediawiki.cookie: Export config via packageFiles by @Krinkle, mediawiki.cookie doesn't use mw.config to retrieve these settings, but rather they are injected via packageFiles. Thus, they should no longer be needed in mw.config.
However, a number of non-deployed extensions still use these, so an entry in the release notes is probably a good idea: https://codesearch.wmcloud.org/search/?q=wgCookie(Prefix%7CDomain%7CPath%7CExpiration)&i=nope&files=%5C.js%24&excludeFiles=&repos=