When an admin registers their site, if they chose to display their site in the site listing, the setting 'Display contact form' appears and they can select 'Yes, provide a form for other Moodlers to contact me'.
In the past, when the list of registered sites was on moodle.net, if a visitor knew to log in (not very intuitive!) when they browsed the list, sites which were willing to be contacted had an icon next to them with a link to a contact form. (It worked well originally, when the list of registered sites was on moodle.org, and people were likely to be logged in anyway.)
The functionality doesn't exist on stats.moodle.org. These days, if sites are willing to be contacted, they provide a contact link on their site.
As the functionality was most likely hardly ever used when the list of registered sites was on moodle.net, it doesn't seem worth adding it to stats.moodle.org. Instead, let's just remove the 'Display contact form' setting in site registration.