Add CSM drop FK migration

lms/djangoapps/courseware/migrations/0009_auto_20190703_1955.py

+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.22 on 2019-07-03 19:55
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('courseware', '0008_move_idde_to_edx_when'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='studentmodulehistory',
+            name='student_module',
+            field=models.ForeignKey(db_constraint=False, on_delete=django.db.models.deletion.CASCADE, to='courseware.StudentModule'),
+        ),
+    ]