title: Do I have to unsubscribe from completed observable?
body: <p>If an observable completes, do I still have to unsubscribe / dispose (in RxJava2) the observable to remove the Observer (prevent memory leaks) or is this handled internally by RxJava once a <code>onComplete</code> or <code>onError</code> event occurs?</p>
  
  <p>what about other types like <code>Single</code>, <code>Completable</code>, <code>Flowable</code> etc.</p>