How to disable Page Attributes dropdown in wp-admin

Removing support for page attributes will prevent that box from appearing…

function remove_page_attribute_support() {
    remove_post_type_support('page','page-attributes');
}
add_action( 'init', 'remove_page_attribute_support' );

… but I don’t know if you need attributes support or not. If you don’t that is the fix.

If you do, you will need to remove the box as per @KrzysiekDrozdz’s answer, but to be able to use those attributes you will have to rebuild that box, the original is here, in such a way that it works for you.