message: Deprecate SequenceFile Dataset
  SequenceFile Dataset was never in good use,
  and the trend of industry aggressively switching from
  self-managed Hadoop system to cloud-vendor provided storage (S3/GCS/etc)
  makes this Dataset format less and less relevant.
  This PR deprecates SequenceFile Dataset
diff: @@ -21,10 +21,16 @@ from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  +import warnings
  +
  from tensorflow_io.hadoop.python.ops.hadoop_dataset_ops import SequenceFileDataset
  from tensorflow.python.util.all_util import remove_undocumented
  +warnings.warn(
  + "SequenceFileDataset is deprecated and will be removed in the next release",
  + DeprecationWarning)
  +
  _allowed_symbols = [
  "SequenceFileDataset",
  ]
  