Use built-in open().

On Python 3, `open is io.open`.

templates/adding_a_new_model/tests/test_tokenization_xxx.py

@@ -16,7 +16,6 @@
 
 import os
 import unittest
-from io import open
 
 from transformers.tokenization_bert import VOCAB_FILES_NAMES, XxxTokenizer
 

templates/adding_a_new_model/tokenization_xxx.py

@@ -18,7 +18,6 @@
 import collections
 import logging
 import os
-from io import open
 
 from .tokenization_utils import PreTrainedTokenizer
 

tests/test_tokenization_bert.py

@@ -16,7 +16,6 @@
 
 import os
 import unittest
-from io import open
 
 from transformers.tokenization_bert import (
     VOCAB_FILES_NAMES,

tests/test_tokenization_bert_japanese.py

@@ -16,7 +16,6 @@
 
 import os
 import unittest
-from io import open
 
 from transformers.tokenization_bert import WordpieceTokenizer
 from transformers.tokenization_bert_japanese import (

tests/test_tokenization_common.py

@@ -18,7 +18,6 @@ import os
 import pickle
 import shutil
 import tempfile
-from io import open
 
 
 class TokenizerTesterMixin:

tests/test_tokenization_ctrl.py

@@ -16,7 +16,6 @@
 import json
 import os
 import unittest
-from io import open
 
 from transformers.tokenization_ctrl import VOCAB_FILES_NAMES, CTRLTokenizer
 

tests/test_tokenization_gpt2.py

@@ -17,7 +17,6 @@
 import json
 import os
 import unittest
-from io import open
 
 from transformers.tokenization_gpt2 import VOCAB_FILES_NAMES, GPT2Tokenizer
 

tests/test_tokenization_roberta.py

@@ -17,7 +17,6 @@
 import json
 import os
 import unittest
-from io import open
 
 from transformers.tokenization_roberta import VOCAB_FILES_NAMES, RobertaTokenizer
 

tests/test_tokenization_transfo_xl.py

@@ -16,7 +16,6 @@
 
 import os
 import unittest
-from io import open
 
 from transformers import is_torch_available