message: Remove the instance checking of `function.ConcreteFunction`.
diff: @@ -25,7 +25,6 @@ import functools
  import weakref
  from tensorflow.python.eager import def_function
  -from tensorflow.python.eager import function
  from tensorflow.python.framework import tensor_shape
  from tensorflow.python.framework import tensor_spec
  from tensorflow.python.keras import backend as K
  @@ -635,6 +634,6 @@ def _wrap_activity_regularizer(layer):
  def _get_layer_call_method(layer):
  - if isinstance(layer.call, (def_function.Function, function.ConcreteFunction)):
  + if isinstance(layer.call, (def_function.Function)):
  return layer.call.python_function
  return layer.call
  