Improve get_page_by_path() performance

[duck_]

Follow up for #17670 where a few performance improvements were suggested.

I found an improvement of about 50% in some simplistic tests (loop over the function 10,000 times) by removing the $post_type parameter from the get_page() call. This was added in [13774]. The issue is that this is passing the post type to the filter argument which means that get_post() runs the relatively expensive sanitize_post().

[nacin]

Per IRC. This is just a copy-paste error. Parameter never should have been passed.

[duck_]

In [19283]:

Don't pass $post_type as get_page()'s $filter argument. Copy-and-paste error. Removal improves get_page_by_path() performance dramatically by stopping sanitize_post() being called. Fixes #19175.