Following T190015, sysops can now longer use their deletedhistory/deletedtext access on css/js pages.
While it is expected that non-interface administrators should not be able to undelete jss/css pages, we do expect that they may still **view ** the deleted history, and even advertise it in the page notice.
> You do not have permission to view a page's deleted history, for the following reason:
> The action you have requested is limited to users in one of the groups: Administrators, Researchers.
Example can be seen here: https://test.wikipedia.org/wiki/Special:Undelete/MediaWiki:TestJs.js (assuming you are a testwiki admin, and not something extra like an interface admin)