Remove phpunit tests for features backported to Core (WordPress#58776)

Co-authored-by: youknowriad <[email protected]>
Co-authored-by: gziolo <[email protected]>
Co-authored-by: jsnajdr <[email protected]>
Co-authored-by: ntsekouras <[email protected]>
Co-authored-by: ramonjd <[email protected]>
Co-authored-by: draganescu <[email protected]>