luci-base: cbi.js: drop CustomEvent polyfill

All supported browsers natively support this functionality since
quite a while already.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

modules/luci-base/htdocs/luci-static/resources/cbi.js

@@ -733,18 +733,6 @@ function matchesElem(node, selector) { return L.dom.matches(node, selector) }
 function findParent(node, selector) { return L.dom.parent(node, selector) }
 function E() { return L.dom.create.apply(L.dom, arguments) }
 
-if (typeof(window.CustomEvent) !== 'function') {
-	function CustomEvent(event, params) {
-		params = params || { bubbles: false, cancelable: false, detail: undefined };
-		var evt = document.createEvent('CustomEvent');
-		    evt.initCustomEvent( event, params.bubbles, params.cancelable, params.detail );
-		return evt;
-	}
-
-	CustomEvent.prototype = window.Event.prototype;
-	window.CustomEvent = CustomEvent;
-}
-
 function cbi_dropdown_init(sb) {
 	if (sb && L.dom.findClassInstance(sb) instanceof L.ui.Dropdown)
 		return;