Revert "Replace anchor.js with jekyll-anchor-headings."

This reverts commit b04f97f60b.

site/docs/4.1/assets/js/src/application.js

@@ -10,7 +10,7 @@
  * details, see https://creativecommons.org/licenses/by/3.0/.
  */
 
-/* global ClipboardJS: false, bsCustomFileInput: false */
+/* global ClipboardJS: false, anchors: false, bsCustomFileInput: false */
 
 (function ($) {
   'use strict'
@@ -101,6 +101,10 @@
         .tooltip('_fixTitle')
     })
 
+    anchors.options = {
+      icon: '#'
+    }
+    anchors.add('.bd-content > h2, .bd-content > h3, .bd-content > h4, .bd-content > h5')
     $('.bd-content').children('h2, h3, h4, h5').wrapInner('<span class="bd-content-title"></span>')
 
     bsCustomFileInput.init()