The script tries to reproduce CIPD behavior when trying to download artifacts from GCS and has been a bit flaky. Instead of trying to reinvent CIPD, we should just use it instead. Except, those artifacts are not currently published to CIPD. The issue dart-lang/sdk#40690 tracks uploading those artifacts. Once that is fixed, this issue tracks removing the script and updating DEPS to use CIPD to fetch the Dart SDK.