fix: prometheus & statsd default config: disable

apps/emqx_prometheus/etc/emqx_prometheus.conf

@@ -4,5 +4,5 @@
 prometheus {
     push_gateway_server = "http://127.0.0.1:9091"
     interval = "15s"
-    enable = true
+    enable = false
 }

apps/emqx_statsd/etc/emqx_statsd.conf

@@ -3,7 +3,7 @@
 ##--------------------------------------------------------------------
 
 statsd {
-    enable = true
+    enable = false
     server = "127.0.0.1:8125"
     sample_time_interval = "10s"
     flush_time_interval = "10s"