drush pm-uninstall [project]
drush pm-uninstall overlay
When you disable a module, it is no longer in use by your site. However, all of the data and configuration that was used by that module is still in the database. If you'd like to clean up your database, and remove the unused data left behind by disabled modules, you'll use the "pm-uninstall" command to uninstall the module. The comparable way to achieve this in the interface is found in the "Uninstall" tab of the modules page.
You can simply type "drush pm-uninstall overlay" to uninstall the overlay. Or, type "drush pm-uninstall overlay admin_menu admin_menu_toolbar toolbar_admin_menu module_filter" to uninstall all of the modules at once. You'll notice that in order to uninstall admin_menu, I need to uninstall admin_menu_toolbar, and toolbar_admin_menu. So, I'll type "y" and push enter. Then type "drush pm-uninstall admin_menu" to uninstall the Admin Menu module.
Now, all of the configuration and data related to the overlay module have been removed from the database, and we can refresh the "Uninstall" page to verify this. This is an important step to take when you disable modules that you no longer use, most importantly, because smaller databases perform better, but another reason is that your backups will be smaller and be completed in less time.