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/document_signatures/views.py

@@ -300,7 +300,7 @@ class DocumentVersionSignatureListView(SingleObjectListView):
             ) % self.get_document_version(),
         }
 
-    def get_queryset(self):
+    def get_object_list(self):
         return self.get_document_version().signatures.all()