*   `converter.convert()` no longer returns a `tf.function`. Now the
        function must be accessed from the saved model.
    *   The `converter.calibrate()` method has been removed. To trigger
        calibration, a `calibration_input_fn` should be provided to
        `converter.convert()`.

*   Other:

    *   Fix accidental quadratic graph construction cost in graph-mode
        `tf.gradients()`.