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 to remove in the wp-config.php file is the following;
define('WP_CACHE', true); // Added by WP Hummingbird
Hummingbird plugin on uninstall will remove the created options it sets on activation.
To ensure all Hummingbird data is removed during uninstall, go to the following admin menu in wp-admin;
Hummingbird > Settings > Data & Settings