migration: Add cleanup-people migration script

Now that we only create Person object once the User has been confirmed,
we can clean up unused Person objects from the database.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

Author: jk-ozlabs

lib/sql/migration/014-cleanup-people.sql

@@ -0,0 +1,7 @@
+BEGIN;
+DELETE FROM patchwork_person WHERE id NOT IN (
+	SELECT submitter_id FROM patchwork_patch
+	UNION
+	SELECT submitter_id FROM patchwork_comment)
+    AND user_id IS NULL;
+COMMIT;