This line requires a file from social plugin. This means that even if you are not using this plugin, you cannot delete it from the plugins folder or the system will crash.

Error shown when deleting social plugin:

Fatal error: require_once(): Failed opening required '../e107_plugins/social/includes/social_login_config.php' (include_path='.;C:/*/php/pear') in C:*\e107_handlers\user_handler.php on line 1113