docs: fix comments in config tempate

apps/emqx_dashboard/etc/emqx_dashboard.conf

@@ -1,12 +1,8 @@
 dashboard {
     listeners {
-        http {
-            ## Comment out 'bind' (or set bind=0) to disable listener.
-            bind = 18083
-        }
+        http.bind = 18083
+        # https.bind = 18084
         https {
-            ## Uncomment to enable
-            # bind = 18084
             ssl_options {
                 certfile = "${EMQX_ETC_DIR}/certs/cert.pem"
                 keyfile = "${EMQX_ETC_DIR}/certs/key.pem"