Remove unused imports and fix some other linter errors.

recipe_engine/fetch.py

 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 import base64
-import functools
 import httplib
 import json
 import logging
 import os
 import shutil
 import sys
 import tarfile
 import tempfile
-import time
 
 # Add third party paths.
 from . import env
 from . import requests_ssl
 from . import util
 from .requests_ssl import requests
 
 import subprocess42
 from google.protobuf import text_format
 
@@ skipping 307 matching lines @@
     logging.info('fetching %s', url)
 
     resp = requests.get(url)
     if resp.status_code != httplib.OK:
       raise GitilesFetchError(resp.status_code, resp.text)
 
     if not resp.text.startswith(cls._GERRIT_XSRF_HEADER):
       raise GitilesFetchError(resp.status_code, 'Missing XSRF header')
 
     return json.loads(resp.text[len(cls._GERRIT_XSRF_HEADER):])