Drop custom file upload plugin in favor of CSS

site/assets/js/application.js

@@ -10,7 +10,7 @@
  * For details, see https://creativecommons.org/licenses/by/3.0/.
  */
 
-/* global ClipboardJS: false, anchors: false, bootstrap: false, bsCustomFileInput: false */
+/* global ClipboardJS: false, anchors: false, bootstrap: false */
 
 (function () {
   'use strict'
@@ -141,6 +141,4 @@
     icon: '#'
   }
   anchors.add('.bd-content > h2, .bd-content > h3, .bd-content > h4, .bd-content > h5')
-
-  bsCustomFileInput.init()
 })()