Remove unused draggable.js file

- Remove draggable.js as the draggability feature already works without and it wasn't used anywhere except in sign.html (which throw an exception already as draggableElement was null, and yet the functionality was working as expected, thus we don't need it)

src/main/resources/templates/sign.html

@@ -236,9 +236,6 @@
     </div>
     <th:block th:insert="~{fragments/footer.html :: footer}"></th:block>
   </div>
-  <!-- Link the draggable.js file -->
-  <script th:src="@{'/js/draggable.js'}"></script>
-
 </body>
 
 </html>