Remove PreserveGetQuerySet mixin. Update SingleObjectList and

MultipleObjectFormActionView views to use a new get_object_list method.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/checkouts/apps.py

@@ -6,7 +6,6 @@ from kombu import Exchange, Queue
 
 from django.apps import apps
 from django.db.models.signals import pre_save
-from django.urls import reverse_lazy
 from django.utils.translation import ugettext_lazy as _
 
 from acls import ModelPermission