It is not a sock puppet, but rather an automated or semi-automated account for making repetitive edits that would be extremely tedious to do manually. Administrators: if this bot is malfunctioning or causing harm, please block it.
Wikidata now stores and serves interwiki links for wikipedia and wikivoyage sites. See d:Q1 and d:Q2 as examples. These pages now hold the interwiki links that could previously be found on Wikipedia projects. As the links are stored in Wikidata there is no longer any need to store them at the bottom of articles.
This bot made millions of edits across all Wikimedia sites removing these interwiki links where they were no longer needed.