Remove extra sanitization before caching in get_pages function

[david.binda]

This ticket is related to #50567 , respectively r53042 , where a filter is set to raw for any post passed through the update_post_cache function.

There is a custom logic in `get_pages()` function for preventing duplicate sanitization of pages before they are cached (introduced in r12062 ), which is now redundant.

IMHO, we can safely remove the custom logic from the function when r53042 is in place.

[spacedmonkey]

This issue was fixed as part of [55569].