Deactivating the Simple:Press Forum plugin and removing the plugin code files does not remove the data tables and option records that the plugin creates and uses.
To completely remove every trace of the plugin (Warning: This will remove all your data!), visit the Forum – Toolbox – Uninstall panel and check the ‘Uninstall’ option. After this is checked and the option is saved, deactivating the plugin will then remove all data from your database. This action cannot be undone.