AngularFire2 is currently undergoing refactoring, and much of its authentication API will be removed in favor of using the Firebase Web API in conjunction with AngularFire2. See this issue for more details.
The watcher you used will remain in AngularFire2, and you can subscribe to it to receive notifications of changes in authentication status.
However, if everything that interests you determines if there is an authenticated user, there is a currentUser property in the Firebase web API that will tell you that:
import * as firebase from "firebase"; ... console.log(firebase.auth().currentUser);
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