De-wiki

Remove all wiki functionality (and metalsmith) in favor of serving up the registration forms as a static HTML pages. The email templates from https://git.coop/social.coop/general have been moved to the templates directory.

This should be merged when https://git.coop/social.coop/tech/ansible/-/merge_requests/28 is merged and prior to it being run.

Fixes #3 (closed)