refactor: replace jquery.are-you-sure with first-party code (#39233)

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/features/common-form.ts

@@ -1,17 +1,7 @@
-import {applyAreYouSure, initAreYouSure} from '../vendor/jquery.are-you-sure.ts';
 import {handleGlobalEnterQuickSubmit} from './comp/QuickSubmit.ts';
 import {queryElems} from '../utils/dom.ts';
 import {initComboMarkdownEditor} from './comp/ComboMarkdownEditor.ts';
 
-export function initGlobalFormDirtyLeaveConfirm() {
-  initAreYouSure(window.jQuery);
-  // Warn users that try to leave a page after entering data into a form.
-  // Except on sign-in pages, and for forms marked as 'ignore-dirty'.
-  if (!document.querySelector('.page-content.user.signin')) {
-    applyAreYouSure('form:not(.ignore-dirty)');
-  }
-}
-
 export function initGlobalEnterQuickSubmit() {
   document.addEventListener('keydown', (e) => {
     if (e.isComposing) return;