Cleaned up unused controller method

- this isn't being used anywhere, so we can clean it up

ghost/core/core/server/api/endpoints/mail.js

@@ -47,24 +47,6 @@ const controller = {
         query(frame) {
             return _private.sendMail(frame.data);
         }
-    },
-
-    sendTest(frame) {
-        return mailService.utils.generateContent({template: 'test'})
-            .then((content) => {
-                const payload = {
-                    mail: [{
-                        message: {
-                            to: frame.user.get('email'),
-                            subject: tpl(messages.testGhostEmail),
-                            html: content.html,
-                            text: content.text
-                        }
-                    }]
-                };
-
-                return _private.sendMail(payload);
-            });
     }
 };