Remove unused legacy Javascript.

* plone_ecmascript/cookie_functions.js
* plone_ecmascript/js-standards.js
* plone_ecmascript/kss-bbb.js
* plone_ecmascript/popupforms.js

updates #282

See also https://github.com/plone/plone.app.controlpanel/pull/32

ping @vangheem @thet