popup: optimize code (#14413)

* getDOM的递归有问题

* Popup: remove useless getDOM function

src/utils/popup/index.js

@@ -8,14 +8,6 @@ let idSeed = 1;
 
 let scrollBarWidth;
 
-const getDOM = function(dom) {
-  if (dom.nodeType === 3) {
-    dom = dom.nextElementSibling || dom.nextSibling;
-    getDOM(dom);
-  }
-  return dom;
-};
-
 export default {
   props: {
     visible: {
@@ -124,7 +116,7 @@ export default {
 
       this._opening = true;
 
-      const dom = getDOM(this.$el);
+      const dom = this.$el;
 
       const modal = props.modal;