We need to cleanup replsettest.js since there are some codes that assume asCluster() is not able to authentication with x509, but this is not the case after the completion of
SERVER-53605. For example here and here. However there are still some cases where asCluster() will not do authentication. So in these cases, another cleanup up might be to enhance the asCluster() API to take an optional parameter that specifies whether asCluster() should run the function if it decides not to do authentication for unauthenticated connections.