remove mail domain add/remove API

merge this as a transaction into domains API

fixes #669

src/routes/test/users-test.js

@@ -47,7 +47,6 @@ function setup(done) {
         server.start,
         database._clear,
         domains.add.bind(null, DOMAIN_0.domain, DOMAIN_0, AUDIT_SOURCE),
-        mail.addDomain.bind(null, DOMAIN_0.domain)
     ], function (error) {
         expect(error).to.not.be.ok();