Notable changes:

* Remove `Jetpack_User_Agent_Info::is_OperaMobile()`. #16434 removed the
  jetpack-device-detect function this was calling in October 2021, but
  missed this caller.
* Remove `jetpack_server_sandbox()` and
  `jetpack_server_sandbox_request_parameters()`. Due to a wrong
  namespace in #21128, they'd have thrown fatals since October 2021.
* Use `$skin` instead of `$upgrader->skin`, it's the same object but not
  typed as a parent class. Should be no change to functionality.
* Add some missing methods to `WPCOM_JSON_API`.
* Add some missing abstract methods to SAL_Site, and implement in
  Jetpack_Site.
* Fix `SAL_Token::is_global()`.
* Remove `views/admin/deactivation-dialog.php`, unused since #21048 in
  November 2021.
* Add `@phan-var-force` in a lot of "template" files. I'm not entirely
  happy with this, it pollutes the global scope for any subsequent files
  processed, but short of writing a Phan plugin that somehow adjusts the
  scope for only the file I can't find a better idea.

…n a different namespace in old phpunit

…entirely, it hasn't been loaded since 11.4.

…ared-issues