remove javascript fetch polyfill

examples/javascript/js_example/templates/plain.html

@@ -1,28 +0,0 @@
-{% extends 'base.html' %}
-
-{% block intro %}
-  <a href="https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest"><code>XMLHttpRequest</code></a>
-  is the plain JavaScript way to make requests. It's natively supported
-  by all browsers.
-{% endblock %}
-
-{% block script %}
-  <script>
-    function addSubmit(ev) {
-      ev.preventDefault();
-      var request = new XMLHttpRequest();
-      request.addEventListener('load', addShow);
-      request.open('POST', {{ url_for('add')|tojson }});
-      request.send(new FormData(this));
-    }
-
-    function addShow() {
-      var data = JSON.parse(this.responseText);
-      var span = document.getElementById('result');
-      span.innerText = data.result;
-    }
-
-    var form = document.getElementById('calc');
-    form.addEventListener('submit', addSubmit);
-  </script>
-{% endblock %}