Update imports in psycopg2.py, extensions.py, and sessions.py

Author: Grimpy101

flask_phpbb3/backends/psycopg2.py

@@ -1,5 +1,3 @@
-from __future__ import absolute_import
-
 import json
 from typing import Any, Dict, List, Optional
 

flask_phpbb3/extension.py

@@ -1,13 +1,11 @@
-from __future__ import absolute_import
-
 import typing
 
 import flask
 
 import flask_phpbb3.backends.base
 import flask_phpbb3.sessions
 
-import werkzeug.contrib.cache
+import cachelib
 
 
 class PhpBB3(object):

flask_phpbb3/sessions.py

@@ -1,5 +1,3 @@
-from __future__ import absolute_import
-
 import json
 import typing
 
@@ -10,7 +8,7 @@
 import flask_phpbb3
 import flask_phpbb3.backends.base
 
-import werkzeug.contrib.cache
+import cachelib
 
 ANONYMOUS_CACHE_TTL = 3600 * 24