Fix F401 flake8 warning (x152 / 268).

This change is mostly autogenerated with:

    $ python -m autoflake --in-place --recursive examples templates transformers utils hubconf.py setup.py

I made minor changes in the generated diff.

templates/adding_a_new_model/configuration_xxx.py

@@ -16,10 +16,7 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
-import json
 import logging
-import sys
-from io import open
 
 import six
 

templates/adding_a_new_model/modeling_tf_xxx.py

@@ -21,14 +21,8 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
-import copy
 import itertools
-import json
 import logging
-import math
-import os
-import sys
-from io import open
 
 import numpy as np
 import tensorflow as tf

templates/adding_a_new_model/modeling_xxx.py

@@ -20,14 +20,9 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
-import copy
 import itertools
-import json
 import logging
-import math
 import os
-import sys
-from io import open
 
 import torch
 from torch import nn

templates/adding_a_new_model/tests/modeling_tf_xxx_test.py

@@ -14,7 +14,6 @@
 # limitations under the License.
 from __future__ import absolute_import, division, print_function
 
-import sys
 import unittest
 
 from transformers import XxxConfig, is_tf_available