Remove rel=”attachment wp-att-XX”

You can remove it right before post is printed to the screen by stripping it out from content. But remember it still will meddle in Editor.

<?php
function my_remove_rel_attr($content) {
    return preg_replace('/\s+rel="attachment wp-att-[0-9]+"/i', '', $content);
}
add_filter('the_content', 'my_remove_rel_attr');