Get rid of old public archive bucket

[sigurdm]

dartlang-pub-public-archives
dartlang-pub-dev-public-archives

We are now serving the package archives out of the exported api bucket. But we still seem to maintain the old public bucket.
We need to:

• Update the deployment script to rely on the exported api bucket instead.
• Make the old bucket private for a week or two, to make sure noone is relying on it
• Remove the updates and any other references to the old bucket
• Remove the old bucket