MiddlewareMixin is always present in django>=3.2

it was added in django 2.0a1

Author: asottile-sentry

csp/middleware.py

@@ -6,21 +6,9 @@
 from functools import partial
 
 from django.conf import settings
+from django.utils.deprecation import MiddlewareMixin
 from django.utils.functional import SimpleLazyObject
 
-try:
-    from django.utils.deprecation import MiddlewareMixin
-except ImportError:
-
-    class MiddlewareMixin(object):
-        """
-        If this middleware doesn't exist, this is an older version of django
-        and we don't need it.
-        """
-
-        pass
-
-
 from csp.utils import build_policy