function plt_hide_post_backgrounds_metaboxes() {
$screen = get_current_screen();
if ( !$screen ) {
return;
}
//Hide the "Post Content Area Background" meta box.
remove_meta_box('postbackground-content', $screen->id, 'normal');
//Hide the "Body Post Background" meta box.
remove_meta_box('postbackground-body', $screen->id, 'normal');
}
add_action('add_meta_boxes', 'plt_hide_post_backgrounds_metaboxes', 20);