lists: fix mdl warnings

In this example, we'll pretend to handle a request to redact the name "Foo Bar"

In this example, we'll pretend to handle a request to redact the name "Foo Bar"

and an associated email address, "foo@bar.com":

and an associated email address, "foo@bar.com":

0. login to `lists-01`, run `sudo -u postgres psql` and `\c mailman3`

 0. Login to `lists-01`, run `sudo -u postgres psql` and `\c mailman3`

1. backup the affected database rows to temporary tables:

 1. Backup the affected database rows to temporary tables:

```

CREATE TEMP TABLE hyperkitty_attachment_redact AS

CREATE TEMP TABLE hyperkitty_attachment_redact AS

SELECT * FROM hyperkitty_attachment

SELECT * FROM hyperkitty_attachment

    WHERE

    WHERE

CREATE TEMP TABLE user_redact AS

CREATE TEMP TABLE user_redact AS

      SELECT * from "user"

      SELECT * from "user"

  WHERE display_name = 'Foo Bar';

  WHERE display_name = 'Foo Bar';

```

2. begin the transaction

 2. Run the actual modifications inside a transaction:

    	BEGIN;

    	BEGIN;

            SET display_name = '[REDACTED]'

            SET display_name = '[REDACTED]'

            WHERE display_name = 'Foo Bar';

            WHERE display_name = 'Foo Bar';

3. look around the modified tables, do `COMMIT;` if all good, otherwise `ROLLBACK;`

 3. Look around the modified tables, do `COMMIT;` if all good, otherwise `ROLLBACK;`

4. ending the `psql` session discards the temporary tables, so keep it open

 4. Ending the `psql` session discards the temporary tables, so keep it open

5. look at the archives if everything is ok

 5. Look at the archives if everything is ok

6. end the `psql` session

 6. End the `psql` session

To rollback changes after the transaction has been committed to the database,

To rollback changes after the transaction has been committed to the database,

using the temporary tables:

using the temporary tables: