If you'd rather not have your activity recorded for posterity, you can either delete your Google+ account (if it's not too late) or else follow the Internet Archive's process for removing specific content.

It's not completely surprising that efforts would be underway to preserve Google+, but it's an unusual situation. You don't see archivists preserving a major social network (albeit one that struggled to compete) very often. The question is whether or not it will be a comprehensive record -- there isn't much time left to safeguard every last ounce of public content.