[swarming] Disable cron_delete_old_bot
[swarming] Disable cron_delete_old_bot

It's currently spinning not doing anything. Let's save some money here.

R=747cf52e0cef2e3e9371802a2d344b6c87126a4b@chromium.org

Bug: 939490
Change-Id: Id8b532d4175d19f1d1bb0fbe99767bd9f6f52a48
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/1509337
Reviewed-by: Quinten Yearsley <747cf52e0cef2e3e9371802a2d344b6c87126a4b@chromium.org>
Commit-Queue: Marc-Antoine Ruel <d2bf0fc09b08f7b0888b3ddab32b3e89c7122c8b@chromium.org>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py