In 2007 (MW 1.10), the `page_restrictions` table was introduced. Rows in this table take precedence over the old `page.page_restrictions` field ([r19095](https://www.mediawiki.org/wiki/Special:Code/MediaWiki/19095)).
Later that year, a maintenance script was introduced to migrate old values (28df3d07e6, [r21455](http://mediawiki.org/wiki/Special:Code/MediaWiki/21455)).
Today, 12 years later, we still require an extra query to `page.page_restrictions` when calling `Title::getRestrictions()`, in addition to the `page_restrictions` table.
Let's finished this forgotten migration and kill off that field.
* [ ] Verify that the maintenance script still works. And update it to modern standards as needed in order to make it suitable for running on large WMF wikis.
* [ ] Ensure the updater is automatically run by the database updater.
* [ ] Run the maintenance script on all WMF wikis.
* [ ] One WMF is migrated, in the next wmf alpha branch after that:
** [ ] Remove all code for queries to the old field.
** [ ] Add schema update that removes the field. (core: T35334, wmf: T60674)
I'm not suggesting we drop the column in prod as it seems low priority. The page tables are very large, and the maintenance script will already null-out this field. However, DBAs can decide what they want to do here.