Since it has been broken since the move to git[1] and is unlikely to have been particularly useful anyway, I've just merged a change[2] to remove the version information (and the 'version' parameter) from the API help. This may result in a warning about an unrecognized parameter.
Also, the 'version' property in the results from action=paraminfo will now be the empty string. It was not removed completely at this time to avoid breaking clients where accessing an undefined property is a fatal error; however, it should be considered deprecated and may be removed in a future version.
Note that version information for MediaWiki as a whole is still available via prop=siteinfo.[3]
[1]: https://bugzilla.wikimedia.org/show_bug.cgi?id=35885 [2]: https://gerrit.wikimedia.org/r/#/c/43622/ [3]: e.g. https://en.wikipedia.org/w/api.php?action=query&meta=siteinfo