Remove unittest.main() in test modules.

This construct isn't used anymore these days.

Running python tests/test_foo.py puts the tests/ directory on
PYTHONPATH, which isn't representative of how we run tests.

Use python -m unittest tests/test_foo.py instead.

tests/test_modeling_tf_bert.py

@@ -14,8 +14,6 @@
 # limitations under the License.
 from __future__ import absolute_import, division, print_function
 
-import unittest
-
 from transformers import BertConfig, is_tf_available
 
 from .test_configuration_common import ConfigTester
@@ -315,7 +313,3 @@ class TFBertModelTest(TFCommonTestCases.TFCommonModelTester):
         for model_name in ["bert-base-uncased"]:
             model = TFBertModel.from_pretrained(model_name, cache_dir=CACHE_DIR)
             self.assertIsNotNone(model)
-
-
-if __name__ == "__main__":
-    unittest.main()