Deprecate gem
Deprecate gem

This gem was only pulled in by Signon and link-checker-api but not used. We've removed the dependency on this gem so now we can archive this repo.

See:

https://github.com/alphagov/signon/pull/1893
https://github.com/alphagov/link-checker-api/pull/534

alphagov/deprecated_columns,alphagov/deprecated_columns,alphagov/deprecated_columns