(stable) Update a very old Phriction migration which incorrectly uses "save()"

Summary:
See https://discourse.phabricator-community.org/t/storage-upgrade-error/3748.

It is broadly unsafe for migrations to use "save()". If the object gains new fields later, the query will include "SET newField = X", which will fail against the old schema which is in the process of being upgraded.

Instead, migrations must issue raw SQL against the schema as it is expected to exist at the time the migration executes.

Migrations have followed this rule for a long time, but this ~6 year old migration was overlooked. Update it to issue a raw query to perform the policy update.

Test Plan: This is somewhat flimsy since rebuilding a genuine reproduction case is messy, but used "bin/storage --apply ..." to at least get the new query to execute against modern Phabricator without issues.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Differential Revision: https://secure.phabricator.com/D21124