Cleanup s3 downloads

[springmeyer]

Now that this repo is deprecated (https://github.com/mapbox/node-cpp11#deprecated) we should also plan to cleanup and delete the s3 assets.

Currently many repo's depend on this (https://github.com/search?utf8=%E2%9C%93&q=node-cpp11+%40mapbox&type=Code) and need updated before they can be deleted. These include:

• node-sqlite3
• node-srs
• mapbox/windows-builds
• node-zipfile - https://github.com/mapbox/node-zipfile/blob/11ac0aca68446d9e13f35c15d1e9c5e5c53ac036/appveyor.yml
• mapbox-studio-classic - https://github.com/mapbox/mapbox-studio-classic/blob/05696f05d84bca80ee1e5c9563db77ecf9199f21/scripts/vendor-node.sh