message: Remove legacy TextSummaryPluginAsset class
  This no longer appears to be used since text_summary was migrated to use the new SummaryMetadata approach.
diff: # ==============================================================================
  """Implements text_summary in TensorFlow, with TensorBoard support.
  -The text_summary is basically a wrapper around the generic tensor_summary,
  -and it uses a TextSummaryPluginAsset class to record which tensor_summaries
  -are readable by the TensorBoard text plugin.
  +The text_summary is a wrapper around the generic tensor_summary that takes a
  +string-type tensor and emits a TensorSummary op with SummaryMetadata that
  +notes that this summary is textual data for the TensorBoard text plugin.
  """
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  -import json
  -
  from tensorflow.core.framework import summary_pb2
  from tensorflow.python.framework import dtypes
  from tensorflow.python.ops.summary_ops import tensor_summary
  -from tensorflow.python.summary import plugin_asset
  PLUGIN_NAME = "text"
  @@ -72,19 +69,3 @@ def text_summary(name, tensor, collections=None):
  summary_metadata=summary_metadata,
  collections=collections)
  return t_summary
  -
  -
  -class TextSummaryPluginAsset(plugin_asset.PluginAsset):
  - """Provides a registry of text summaries for the TensorBoard text plugin."""
  - plugin_name = "tensorboard_text"
  -
  - def __init__(self):
  - self._tensor_names = []
  -
  - def register_tensor(self, name):
  - """Register a new Tensor Summary name as containing textual data."""
  - self._tensor_names.append(name)
  -
  - def assets(self):
  - """Store the tensors registry in a file called tensors.json."""
  - return {"tensors.json": json.dumps(self._tensor_names)}
  