Disable dataset threading by default
Disable dataset threading by default

I am running into out of memory issues when using `tf.distribute` with TensorFlow datasets. Disabling this option fixes the issues for me. Unfortunately this option cannot be disabled by the user with `experimental_threading.private_threadpool_size=None` since the option expects an integerl, or am I missing something.
What is the exact benifit of this option, is it essential for a high performance data pipeline? In my initial testing I didn't see any performance regressions when disabling this option.

I created an TensorFlow issue explaining the memory problems in detail: https://github.com/tensorflow/tensorflow/issues/38617
tensorflow/datasets,tensorflow/datasets,tensorflow/datasets,tensorflow/datasets,tensorflow/datasets