add reverse operation

Signed-off-by: tdruez <tdruez@aboutcode.org>

Author: tdruez

vulnerabilities/migrations/0009_api_v3_data_migrations.py

@@ -25,12 +25,18 @@ def migrate_and_purge_vulnerabilities(apps, schema_editor):
     Vulnerability.objects.exclude(id__in=linked_ids).delete()
 
 
+def purge_vulnerabilities(apps, schema_editor):
+    """Purge all vulnerabilities on reverse, data cannot be recovered."""
+    Vulnerability = apps.get_model("vulnerabilities", "Vulnerability")
+    Vulnerability.objects.all().delete()
+
+
 class Migration(migrations.Migration):
 
     dependencies = [
         ('vulnerabilities', '0008_api_v3_new_fields'),
     ]
 
     operations = [
-        migrations.RunPython(migrate_and_purge_vulnerabilities, migrations.RunPython.noop),
+        migrations.RunPython(migrate_and_purge_vulnerabilities, purge_vulnerabilities),
     ]