message: remove duplicate namespace-id and binding args
diff: @@ -160,10 +160,6 @@ fn run() -> Result<(), failure::Error> {
  .arg(kv_namespace_id_arg.clone())
  .group(kv_namespace_specifier_group.clone())
  .arg(environment_arg.clone())
  - .group(ArgGroup::with_name("namespace-specifier")
  - .args(&["binding", "namespace-id"])
  - .required(true)
  - )
  .arg(
  Arg::with_name("key")
  .help("Key whose value to get")
  