generate_header

The generate_header hook is inside your header.php and is where your entire header element is hooked into.

It sits between the generate_before_header and generate_after_header hook.

You can use this hook to completely remove the <header> element from your page:

add_action( 'after_setup_theme','tu_remove_header' );
function tu_remove_header() {
    remove_action( 'generate_header','generate_construct_header' );
}

Learn how to add PHP here.