robots.txt is really only supposed to be used for blocking the Internet Archives first snapshot, and not to remove existing snapshots – and even this might not be the case in the future as they try to preserve most snapshots. They made a few policy changes last year[1] to how they handle robots.txt files, to handle cases where a domain is sold and a new robots.txt file would result in deleting old data among other things.
[1]: https://blog.archive.org/2017/04/17/robots-txt-meant-for-sea...