Hummingbird is a caching and performance plugin with over 70k active installs, but the plugin can cause issues and does not work well as a page caching plugins. The plugin deactivation in Hummingbird will not delete the advanced-cache.php drop in it adds, nor will it remove the constant added into your site wp-config.php. The file to remove if you no longer want to use Hummingbird and use another lightweight solution is; wp-cache.php in the wp-content/wphb-cache folder. You can delete the wphb-cache folder from the wp-content folder on the site server. The other file that Hummingbird will create is; The constant