Disable Prometheus in singleplayer mode

src/server.cpp

@@ -262,10 +262,13 @@ Server::Server(
 		throw ServerError("Supplied invalid gamespec");
 
 #if USE_PROMETHEUS
-	m_metrics_backend = std::unique_ptr<MetricsBackend>(createPrometheusMetricsBackend());
+	if (!simple_singleplayer_mode)
+		m_metrics_backend = std::unique_ptr<MetricsBackend>(createPrometheusMetricsBackend());
+	else
 #else
-	m_metrics_backend = std::make_unique<MetricsBackend>();
+	if (true)
 #endif
+		m_metrics_backend = std::make_unique<MetricsBackend>();
 
 	m_uptime_counter = m_metrics_backend->addCounter("minetest_core_server_uptime", "Server uptime (in seconds)");
 	m_player_gauge = m_metrics_backend->addGauge("minetest_core_player_number", "Number of connected players");