Remove unused imports and fix some other linter errors.

recipe_engine/unittests/stream_logdog_test.py

 #!/usr/bin/env python
 # Copyright 2015 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 collections
 import contextlib
 import datetime
 import json
 import os
 import shutil
 import tempfile
 import threading
 import time
 import unittest
 import StringIO
 
 import test_env
 
 import libs.logdog.stream
 import libs.logdog.varint
 from google.protobuf import json_format as jsonpb
 from recipe_engine import recipe_api
-from recipe_engine import stream
 from recipe_engine import stream_logdog
 
 
 import annotations_pb2 as pb
 
 
 @contextlib.contextmanager
 def tempdir():
   tdir = tempfile.mkdtemp(suffix='stream_logdog_test', dir=test_env.BASE_DIR)
   try:
@@ skipping 987 matching lines @@
     sn = sn.append('#!!! stream name !!!')
     self.assertEqual(str(sn), 'base/s______stream_name____')
 
   def testAugmentInvalidStreamNameNormalizes(self):
     sn = stream_logdog._StreamName('base')
     self.assertEqual(str(sn.augment(' !!! other !!! ')), 'base_____other_____')
 
 
 if __name__ == '__main__':
   unittest.main()