title: SASS remove unneeded class
body: <p>I @import something from bootstrap-sass like </p>
  
  <pre><code>@import 'bootstrap-sass/assets/stylesheets/bootstrap/buttons';
  </code></pre>
  
  <p>Then next I extend it to someother name to avoid conflicts when used on an existing web site.</p>
  
  <pre><code>.my-cus-btn {
    @extend .btn
  }
  </code></pre>
  
  <p>Question now is how can I remove the default .btn in order to avoid messup with existing website/css when used?</p>
  
  <p>Ps: to make it clear, I want the final CSS contains only .my-cus-btn but NO .btn, otherwise this style sheet will mess up legacy code.</p>
  
  <p>But I really want to base on bootstrap-sass or similar framework </p>