title: Delete local Git branches if their remote-tracking references don't exist anymore
body: <p>I have a local and a remote Git repository.</p>
  
  <ul>
  <li><p>In my local repository I create and switch to a new branch: <code>git checkout -b feature/niceNewFeature</code></p></li>
  <li><p>I do my coding, <code>git add .</code>, <code>git commit</code> and <code>git push</code> my <code>feature/niceNewFeature</code> branch to the remote repository (e.g. GitHub).</p></li>
  <li><p>After this I create a GitHub Pull Request to merge <code>feature/niceNewFeature</code> branch into <code>master</code> - after the code is reviewed, I will do so.</p></li>
  <li><p>Since <code>feature/niceNewFeature</code> is now merged to <code>master</code>, I will delete it on GitHub. </p></li>
  <li><p>However, in my local repository, feature/niceNewFeature branch is still listed if I execute <code>git branch</code> command.</p></li>
  </ul>
  
  <p>How do I remove <code>feature/niceNewFeature</code> branch from my local repository, since it is already merged to <code>master</code> and deleted from the remote repository?</p>