I doubt it very much. It is not a violation of the Constitution for the owner of a website to remove user-generated content. It happens all the time and has never been ruled to be unconstitutional.
> ... Cryptographer Matthew Green noted that, but also pointed out the irony of removing code from a distributed, decentralized revision-control system like Git. ...
GitHub != Git. And GitHub is not decentralized in anywhere close to the sense that Git is. I'm not sure where this author is getting their information from, but seems to be just repeating, uncritically, things said on the internet.