"What prosecutors?"? What do you imagine the difference is between saying "prosecutors need to lose their immunity" and "we need to lose prosecutorial immunity"?
Note the caption: Rubin v. New Jersey. Rubin is the plaintiff. The AG is acting in its capacity as the government's lawyer, not in its capacity as a prosecutor. There is no prosecutor, because there is no criminal complaint. What's at issue is a civil subpoena (a request for information and materials) issued by a state consumer protection agency.
All prosecutors, obviously.