|Reported by:||nacin||Owned by:||nacin|
Dashboard widgets should simply go through the standard ajax handler.
See also #18952 where ajaxurl is now relative. This allows us to simply move to ajaxurl rather than the existing .replace() we use to turn admin-ajax.php into index-extra.php.
We can also remove the network/index-extra.php and user/index-extra.php files, which actually aren't used.