remove Python2 crumbs (#262)

* use new unittest.mock everywhere, not only in accountAdmin/base.py

* remove old "from __future__ import" statements

* remove six, pyflakes

.github/workflows/publish.yml

@@ -21,7 +21,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install setuptools wheel twine six
+        pip install setuptools wheel twine
     - name: Generate SBOM
       run: |
         pip install cyclonedx-bom==3.11.7

duo_client/__init__.py

@@ -1,4 +1,3 @@
-from __future__ import absolute_import
 from .accounts import Accounts
 from .admin import Admin
 from .auth import Auth

duo_client/accounts.py

@@ -3,7 +3,6 @@
 
 <http://www.duosecurity.com/docs/accountsapi>
 """
-from __future__ import absolute_import
 from . import client
 
 class Accounts(client.Client):