class Greeter {

    String getGreeting() {
        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
    }

}

class Greeter {

    String getGreeting() {
        return "Goodbye, Mars!";
    }

}

Simplify the `hello-world` exercise's stub. The goal of this is to make things easier for students to get started and to introduce as little syntax as possible. (#1950)