remove mail domain add/remove API

merge this as a transaction into domains API

fixes #669

src/test/mail-test.js

@@ -34,7 +34,6 @@ function setup(done) {
         database._clear,
         domains.add.bind(null, DOMAIN_0.domain, DOMAIN_0, AUDIT_SOURCE),
         settings.setAdmin.bind(null, DOMAIN_0.domain, 'my.' + DOMAIN_0.domain),
-        mail.addDomain.bind(null, DOMAIN_0.domain)
     ], done);
 }