No, there's no way to put turn it off because that's how the "Report to moderator" functions but I believe it is used to track the number of reports made by each user.
Seriously, I've wondered what's the need to expose reporters' emails since notes and responses to the report can be sent to reporters through PMs. It makes it look like exposing the privacy of those who use the "report to moderators" tab. It's like reporting a criminal at a police station and then police ask you to write down your name and address. It doesn't make sense, honestly. On a few occasions my posts were deleted, I got reports in pm here in the forum. So, it shows that asking for emails can be avoided and it won't destabilize the forum