message: Address lint errors in callbacks.py.
  Deprecate callback.validation_data attribute as it was removed in a previous change and there's nothing remaining in tf.keras that uses it.
diff: @@ -421,6 +421,7 @@ class Callback(object):
  (eg. verbosity, batch size, number of epochs...).
  model: instance of `keras.models.Model`.
  Reference of the model being trained.
  + validation_data: Deprecated. Do not use.
  The `logs` dictionary that callback methods
  take as argument will contain keys for quantities relevant to
  @@ -1342,7 +1343,7 @@ class TensorBoard(Callback):
  A writer will be created if it does not yet exist.
  - Args:
  + Arguments:
  writer_name: The name of the directory for which to create or
  retrieve a writer. Should be either `self._train_run_name` or
  `self._validation_run_name`.
  @@ -1365,6 +1366,10 @@ class TensorBoard(Callback):
  """Writes scalar summaries for metrics on every training batch.
  Performs profiling if current batch is in profiler_batches.
  +
  + Arguments:
  + batch: Integer, index of batch within the current epoch.
  + logs: Dict. Metric results for this batch.
  """
  # Don't output batch_size and batch number as TensorBoard summaries
  logs = logs or {}
  