Disable update_default_builders cron job, it's broken.
Disable update_default_builders cron job, it's broken.

Review: https://codereview.appspot.com/7977043/

nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra