tests: remove warning (#21290)

tests/test_api.py::TestApp
    cannot collect test class 'TestApp' because it has a __init__ constructor

tests/test_api.py

@@ -2,7 +2,6 @@ import datetime
 import pytest
 import sys
 import urlparse
-from webtest import TestApp
 
 from django.contrib.auth import get_user_model
 from django.db import connection

tests/test_manager.py

@@ -6,7 +6,7 @@ import datetime
 import mock
 import pytest
 import requests
-from webtest import TestApp, Upload
+from webtest import Upload
 
 from chrono.wsgi import application
 

tests/test_sso.py

@@ -1,5 +1,4 @@
 import pytest
-from webtest import TestApp
 
 from django.test import override_settings