message: Keras TPU support: Fix minior usability issue.
  The current code fails with the following code:
  use_pipeline = magic_function()
  model.fit(..., _pipeline=use_pipeline)
  when use_pipeline is True, it's not pop out from kwargs thus causing exceptions in line 1559
diff: @@ -1482,10 +1482,12 @@ class KerasTPUModel(models.Model):
  self._numpy_to_infeed_manager_list = infeed_managers
  try:
  - if not kwargs.get('_pipeline', True):
  - logging.info('Running non-pipelined training loop (`_pipeline=%s`).',
  - kwargs['_pipeline'])
  + pipeline = kwargs.get('_pipeline', True)
  + if '_pipeline' in kwargs:
  kwargs.pop('_pipeline')
  + if not pipeline:
  + logging.info('Running non-pipelined training loop (`_pipeline=%s`).',
  + pipeline)
  return super(KerasTPUModel, self).fit(
  x, y, batch_size, epochs, verbose, callbacks, validation_split,
  validation_data, shuffle, class_weight, sample_weight,
  