http://docs.vanillaforums.com/addons/reporting/
Do we have "advanced notification" permissions? Maybe you can turn that off?.
Then again, the code itself suggests a different permission:
https://github.com/vanilla/vanilla/blob/master/plugins/Flagging/class.flagging.plugin.php
Maybe it's an artifact from the change to vanilla? We don't see the option because we don't have the Flagging permission, yet we're in the list. Perhaps simply saving the plugin settings will reset the receivers? Either way, there appears to be a config containing our accounts: Plugins.Flagging.NotifyUsers
Happy to take a look if you need another moderator. But this sounds/looks like an admin issue.