Minor migration tweaks

Using migrations.RunPython.noop function instead of a lambda.

ECOM-5173 and ECOM-5189

course_discovery/apps/course_metadata/migrations/0013_auto_20160809_1259.py

@@ -82,7 +82,7 @@ class Migration(migrations.Migration):
             name='subject',
             unique_together=set([('partner', 'name'), ('partner', 'slug'), ('partner', 'uuid')]),
         ),
-        migrations.RunPython(update_subjects, lambda *args: None),
+        migrations.RunPython(update_subjects, reverse_code=migrations.RunPython.noop),
         migrations.AlterField(
             model_name='subject',
             name='slug',

course_discovery/apps/edx_catalog_extensions/migrations/0002_convert_program_category_to_type.py

@@ -18,5 +18,5 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
-        migrations.RunPython(set_program_types, lambda *args: None)
+        migrations.RunPython(set_program_types, reverse_code=migrations.RunPython.noop)
     ]