Changes the mixin's delete algorithm.

openedx/core/djangolib/model_mixins.py

@@ -32,5 +32,10 @@ class DeletableByUserValue(object):
         Returns False otherwise.
         """
         filter_kwargs = {field: value}
-        num_deleted_records, _ = cls.objects.filter(**filter_kwargs).delete()
-        return num_deleted_records > 0
+        records_matching_user_value = cls.objects.filter(**filter_kwargs)
+
+        if not records_matching_user_value.exists():
+            return False
+
+        records_matching_user_value.delete()
+        return True