TLD rewrites are now deprecated

We should add the root domain (aka "tld") as the host or an alias to the site.
They can then point the A records at our CDN Anycast IPs and they will be
redirected by Bouncer. Those IPs are:

23.235.33.144

and:

23.235.37.144
Merge pull request #968 from alphagov/deprecate_tld_rewrites

TLD rewrites are now deprecated