Remove the instance type checking for function.Function.

PiperOrigin-RevId: 358744545
Change-Id: I6586d4986ed5777b2f7130d757c9638996bef789

tensorflow/python/keras/layers/recurrent_v2.py

@@ -1792,9 +1792,6 @@ def _function_register(func, *args, **kwargs):
   Raises:
     ValueError: When the input function is not a defun wrapped python function.
   """
-  if not isinstance(func, function.Function):
-    raise ValueError('Only defun function is allowed to be registered. '
-                     'Got type: %s' % type(func))
   concrete_func = func.get_concrete_function(*args, **kwargs)
   concrete_func.add_to_graph()
   concrete_func.add_gradient_functions_to_graph()

tensorflow/python/keras/saving/saved_model/serialized_attributes.py

@@ -19,7 +19,6 @@ from __future__ import division
 from __future__ import print_function
 
 from tensorflow.python.eager import def_function
-from tensorflow.python.eager import function as defun
 from tensorflow.python.keras.saving.saved_model import constants
 from tensorflow.python.keras.utils.generic_utils import LazyLoader
 from tensorflow.python.training.tracking import base as trackable
@@ -190,8 +189,7 @@ class SerializedAttributes(object):
     for key in self.all_functions:
       if key in function_dict:
         if (function_dict[key] is not None and  # Not all functions are required
-            not isinstance(function_dict[key],
-                           (defun.Function, def_function.Function))):
+            not isinstance(function_dict[key], def_function.Function)):
           raise ValueError(
               'Function dictionary contained a non-function object: {} (for key'
               ' {})'.format(function_dict[key], key))