message: Finish deleting `is_single_replica`. Implementation is currently broken,
  since it accesses the `is_single_replica` property of DistributionStrategy,
  which no longer exists.
diff: @@ -415,9 +415,7 @@ class DistributionStrategy(object):
  You may use this API whether or not a `DistributionStrategy` is
  being used, since there is a default implementation of
  - `ReplicaContext` and `DistributionStrategy`. Or you can use the
  - `get_replica_context().is_single_replica` property to run different code
  - in the distributed vs. single replica cases.
  + `ReplicaContext` and `DistributionStrategy`.
  """
  # TODO(josh11b): Raise an exception if variable partitioning requested before
  @@ -1059,12 +1057,6 @@ class ReplicaContext(object):
  finally:
  _pop_per_thread_mode()
  - @property
  - def is_single_replica(self):
  - """Returns whether there is a single replica or multiple."""
  - require_replica_context(self)
  - return self._distribution_strategy.is_single_replica
  -
  @property
  def num_replicas(self):
  """Returns number of replicas, for purposes of averaging across replicas."""
  