We are removing the `PhabricatorEventType::TYPE_CONTROLLER_CHECKREQUEST` event.
This event was implemented in D2488 to provide some sort of unspecified "checking" of requests (IP-based?), but I believe no install other than Facebook has ever had a use case for it.
In modern Phabricator, the "Preamble Script" can perform this class of checks more broadly, and is required for other request adjustments (header fiddling, HTTPS tweaks):
https://secure.phabricator.com/book/phabricator/article/configuring_preamble/