WordPress can add a lot of stuff in your header for various services, this will remove everything, but take care, it also removes some functionality ( for instance if someone is looking for your RSS feed). If you want to keep some just comment the line out.

remove_header_output.php

<?php

// remove junk from head
remove_action('wp_head', 'feed_links', 2);
remove_action('wp_head', 'feed_links_extra', 3);
remove_action('wp_head', 'rsd_link');
remove_action('wp_head', 'wlwmanifest_link');
remove_action('wp_head', 'index_rel_link');
remove_action('wp_head', 'parent_post_rel_link', 10, 0);
remove_action('wp_head', 'start_post_rel_link', 10, 0);
remove_action('wp_head', 'adjacent_posts_rel_link_wp_head', 10, 0);
remove_action('wp_head', 'wp_generator');
remove_action('wp_head', 'wp_shortlink_wp_head', 10, 0);
remove_action('wp_head', 'noindex', 1);

?>