How to clean up wp_head() without a plugin

Paste the following lines of code into your functions.php file:

remove_action( 'wp_head', 'rsd_link' ); 
remove_action( 'wp_head', 'wlwmanifest_link' ); 
remove_action( 'wp_head', 'wp_generator' ); 
remove_action( 'wp_head', 'start_post_rel_link' ); 
remove_action( 'wp_head', 'index_rel_link' ); 
remove_action( 'wp_head', 'adjacent_posts_rel_link' ); 
remove_action( 'wp_head', 'wp_shortlink_wp_head' );