Extend the use of ResizeObserver by dropping all knockoutjs observable this.resizerTrigger in mail composer

As benefit this also drops the CustomEvent('resize.real')

dev/App/Abstract.js

@@ -31,20 +31,6 @@ class AbstractApp extends AbstractBoot {
 		this.isLocalAutocomplete = true;
 		this.lastErrorTime = 0;
 
-		addEventListener(
-			'resize',
-			(()=>{
-				const iH = $win.height(),
-					iW = $win.height();
-
-				if ($win.__sizes[0] !== iH || $win.__sizes[1] !== iW) {
-					$win.__sizes[0] = iH;
-					$win.__sizes[1] = iW;
-					dispatchEvent(new CustomEvent('resize.real'));
-				}
-			}).throttle(50)
-		);
-
 		const $doc = document;
 		$doc.addEventListener('keydown', (event) => {
 			if (event && event.ctrlKey) {

dev/App/User.js

@@ -80,31 +80,6 @@ import { AbstractApp } from 'App/Abstract';
 
 const doc = document;
 
-if (!window.ResizeObserver) {
-	window.ResizeObserver = class {
-		constructor(callback) {
-			callback = callback.debounce(250);
-			this.observer = new MutationObserver(mutations => {
-				let i = mutations.length;
-				while (i--) {
-					if ('style' == mutations[i].attributeName) {
-						callback();
-						break;
-					}
-				}
-			});
-		}
-
-		disconnect() {
-			this.observer.disconnect();
-		}
-
-		observe(target) {
-			this.observer.observe(target, { attributes: true });
-		}
-	};
-}
-
 class AppUser extends AbstractApp {
 	constructor() {
 		super(Remote);