Instead of deleting bad versions, just tag them as bad.

Summary:
They'll still get reaped by audit_gae_versions, which already knows
about the <version>-bad tag, but this way you can do post-facto
analysis on them, or re-set them as default if they're actually ok,
etc.

Test Plan: Fingers crossed.

Reviewers: chris

Reviewed By: chris

Differential Revision: http://phabricator.khanacademy.org/D12826