function plt_hide_simple_multiple_featured_images_metaboxes() {
$screen = get_current_screen();
if ( !$screen ) {
return;
}
//Hide the "More Featured Images" meta box.
remove_meta_box('smfi-metabox', $screen->id, 'normal');
}
add_action('add_meta_boxes', 'plt_hide_simple_multiple_featured_images_metaboxes', 20);