Merge pull request #10493 from zhongwencool/remove-dashboard-default-username-conf

chore: remove dashboard's default username from emqx.conf

apps/emqx_dashboard/etc/emqx_dashboard.conf

@@ -2,6 +2,4 @@ dashboard {
     listeners.http {
         bind = 18083
     }
-    default_username = "admin"
-    default_password = "public"
 }