rename urllib3 patch method and rm unused imports from tests

tests/integration/test_urllib3.py

@@ -2,12 +2,10 @@
 
 # coding=utf-8
 
-import os
 import pytest
 import vcr
 from assertions import (
     assert_cassette_empty,
-    assert_cassette_has_one_response,
     assert_is_json
 )
 certifi = pytest.importorskip("certifi")