message: Update head.py
  Update contrib lookup to core lookup
diff: @@ -24,7 +24,6 @@ import six
  from tensorflow.contrib import framework as framework_lib
  from tensorflow.contrib import layers as layers_lib
  -from tensorflow.contrib import lookup as lookup_lib
  from tensorflow.contrib.learn.python.learn.estimators import constants
  from tensorflow.contrib.learn.python.learn.estimators import model_fn
  from tensorflow.contrib.learn.python.learn.estimators import prediction_key
  @@ -35,6 +34,7 @@ from tensorflow.python.framework import sparse_tensor
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import control_flow_ops
  from tensorflow.python.ops import logging_ops
  +from tensorflow.python.ops import lookup_ops
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import metrics as metrics_lib
  from tensorflow.python.ops import nn
  @@ -1070,8 +1070,7 @@ class _MultiClassHead(_SingleHead):
  labels_tensor = _to_labels_tensor(labels, self._label_name)
  _check_no_sparse_tensor(labels_tensor)
  if self._label_keys:
  - table = lookup_lib.string_to_index_table_from_tensor(
  - mapping=self._label_keys,
  + table = lookup_ops.index_table_from_tensor(self._label_keys,
  name="label_id_lookup")
  return {
  "labels": labels_tensor,
  @@ -1106,9 +1105,8 @@ class _MultiClassHead(_SingleHead):
  class_ids = math_ops.argmax(
  logits, 1, name=prediction_key.PredictionKey.CLASSES)
  if self._label_keys:
  - table = lookup_lib.index_to_string_table_from_tensor(
  - mapping=self._label_keys,
  - name="class_string_lookup")
  + table = lookup_ops.index_to_string_table_from_tensor(
  + self._label_keys, name="class_string_lookup")
  classes = table.lookup(class_ids)
  else:
  classes = class_ids
  