@Override
  public OperationCallable<DeleteNodeRequest, Empty, OperationMetadata>
      deleteNodeOperationCallable() {
    return deleteNodeOperationCallable;
  }
Constructs an instance of GrpcTpuStub, using the given settings. This is protected so that it
is easy to make a subclass, but otherwise, the static factory methods should be preferred.
java-tpu/google-cloud-tpu/src/main/java/com/google/cloud/tpu/v2alpha1/stub/GrpcTpuStub.java