title: delete cookie key value pair
body: <p>I am trying to delete a cookie by setting the expiry date time as follows. However the key of the cookie still exists. This only sets the cookie to the empty string. How to remove the key value pair of the cookie completely?</p>
  
  <pre><code>document.cookie = "username=; expires=Thu, 01 Jan 1970 00:00:00 UTC";
  </code></pre>