function remove_meta_boxes() {
        // posts
         remove_meta_box('postcustom','post','normal');
         remove_meta_box('trackbacksdiv','post','normal');
         remove_meta_box('commentstatusdiv','post','normal');
         remove_meta_box('commentsdiv','post','normal');
         remove_meta_box('categorydiv','post','normal');
         remove_meta_box('tagsdiv-post_tag','post','normal');
         remove_meta_box('slugdiv','post','normal');
         remove_meta_box('authordiv','post','normal');
        // pages
         remove_meta_box('postcustom','page','normal');
         remove_meta_box('commentstatusdiv','page','normal');
         remove_meta_box('trackbacksdiv','page','normal');
         remove_meta_box('commentsdiv','page','normal');
         remove_meta_box('slugdiv','page','normal');
         remove_meta_box('authordiv','page','normal');
}
add_action('admin_init','remove_meta_boxes');
/* REMOVE SUBMENUS */
//function adjust_the_wp_menu() {
        //$page = remove_submenu_page('edit.php', 'edit-tags.php?taxonomy=post_tag' );
//}
//add_action('admin_menu', 'adjust_the_wp_menu', 999);

Remove/unset native meta boxes

Remove native meta boxes

wordpress

PHP