Set post title to same value as a tow meta box

Why do you need to remove the title? Generally it’s a bad idea, as the title generates the permalink, can’t think of any scenario where it would be necessary.

Anyways, here is some code that looks like it does what you need:

function add_custom_title( $data, $postarr ) {
    if($data['post_type'] == 'myposttype') {
        if(empty($data['post_title']) {
            // here would go the code to construct your custom title
            $data['post_title'] = 'my post title';
        }
    }
    return $data;
}

add_filters('wp_insert_post_data', 'add_custom_title', 10, 2 );

src: http://premium.wpmudev.org/forums/topic/assign-default-title-to-custom-post-types