Remove explicit back_prop=False in decoding loop
It seems to not make a difference in TensorFlow 2.x.
Related to
@@ -482,7 +482,6 @@ def dynamic_decode(symbols_to_logits_fn,
initial_log_probs.shape,
tf.nest.map_structure(_get_shape_invariants, extra_vars)),
parallel_iterations=1,
- back_prop=False,
maximum_iterations=maximum_iterations)
ids, attention, lengths = decoding_strategy._finalize( # pylint: disable=protected-access
