Nigel,
JFBConnect is recommending those settings be blank because an SSL certificate is not installed on your server. Without that, the Page Tab or Canvas features of JFBConnect will not work because Facebook requires sites to use SSL for that functionality.
JFBConnect *should* be able to delete those fields for you if you blank them out and hit "Save Settings". There was a bug on v5.1.0 that prevented the saving of blank fields though, so you'd need to do that with v5.1.2.
Alternatively, in the Facebook Developer Area, instead of blanking those fields out, hit the small 'x' in the top right corner of those sections. That will remove all the settings entirely for those features and then you can hit "Save".
I hope that helps, but if not, let me know.
Thanks,
Alex