remove attribute provider in SQL plugin destruction

src/charon/plugins/sql/sql_plugin.c

@@ -68,6 +68,7 @@ static void destroy(private_sql_plugin_t *this)
 {
 	charon->backends->remove_backend(charon->backends, &this->config->backend);
 	charon->credentials->remove_set(charon->credentials, &this->cred->set);
+	charon->attributes->remove_provider(charon->attributes, &this->attribute->provider);
 	charon->bus->remove_listener(charon->bus, &this->logger->listener);
 	this->config->destroy(this->config);
 	this->cred->destroy(this->cred);