🐛(backend) remove permissions hack

As DRF encode/django-rest-framework#8009 has
been reverted in 3.15.1, the related hack is no longer needed.

src/backend/joanie/core/api/admin/__init__.py

@@ -41,14 +41,6 @@ class OrganizationViewSet(viewsets.ModelViewSet):
     filterset_class = filters.OrganizationAdminFilterSet
     ordering_fields = ["created_on"]
 
-    def get_permissions(self):
-        """
-        Instantiates and returns the list of permissions that this view requires.
-        """
-        if self.action in ["list", "retrieve"]:
-            return [permissions.IsAdminUser()]
-        return super().get_permissions()
-
     def get_serializer_class(self):
         """
         Return the serializer class to use depending on the action.