title: The result of subscribe is not used
body: <p>I've upgraded to Android Studio 3.1 today, which seems to have added a few more lint checks. One of these lint checks is for one-shot RxJava2 <code>subscribe()</code> calls that are not stored in a variable. For example, getting a list of all players from my Room database:</p>
  
  <pre><code>Single.just(db)
              .subscribeOn(Schedulers.io())
              .subscribe(db -&gt; db.playerDao().getAll());
  </code></pre>
  
  <p>Results in a big yellow block and this tooltip:</p>
  
  <blockquote>
    <p>The result of <code>subscribe</code> is not used</p>
  </blockquote>
  
  <p><a href="https://i.stack.imgur.com/UThmL.png" rel="noreferrer"><img src="https://i.stack.imgur.com/UThmL.png" alt="Screenshot of Android Studio. Code is highlighted in Yellow with a tooltip. Tooltip text: The result of subscribe is not used."></a></p>
  
  <p>What is the best practice for one-shot Rx calls like this? Should I keep hold of the <code>Disposable</code> and <code>dispose()</code> on complete? Or should I just <code>@SuppressLint</code> and move on?</p>
  
  <p>This only seems to affect RxJava2 (<code>io.reactivex</code>), RxJava (<code>rx</code>) does not have this lint.</p>