Remove migration deleting XBlockDisableConfig model.

common/djangoapps/xblock_django/migrations/0004_delete_xblock_disable_config.py

-# -*- coding: utf-8 -*-
-from __future__ import unicode_literals
-
-from django.db import migrations, models
-
-
-class Migration(migrations.Migration):
-
-    dependencies = [
-        ('xblock_django', '0003_add_new_config_models'),
-    ]
-
-    operations = [
-        migrations.RemoveField(
-            model_name='xblockdisableconfig',
-            name='changed_by',
-        ),
-        migrations.DeleteModel(
-            name='XBlockDisableConfig',
-        ),
-    ]