Filter Hook: wp_dropdown_cats

On the All Posts page, there are a series of filters for narrowing down what posts are displayed.

To remove the categories filter, use this:

add_action( 'load-edit.php', 'no_category_dropdown' );
function no_category_dropdown() {
	add_filter( 'wp_dropdown_cats', '__return_false' );
}

In the action hook, change ‘edit.php’ if you want to remove the dropdown on other pages.