S: use DELETE FROM ... USING syntax
S: use DELETE FROM ... USING syntax

may improve the performance when the deletable_builds CTE is large

Signed-off-by: Aidan Oldershaw <30ef7a6e0d016bc846f26d89dacbd23aceded206@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse