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.

utils/download_glue_data.py

@@ -20,9 +20,7 @@ rm MSRParaphraseCorpus.msi
 
 import argparse
 import os
-import shutil
 import sys
-import tempfile
 import urllib.request
 import zipfile