Revert "fix: also set ssrAppId for first Vue app when ssrAttribute exists"

This reverts commit 4cb57240da.

examples/ssr/App.js

@@ -66,7 +66,8 @@ export default function createApp () {
     ]
   })
 
-  const App = ({
+  const app = new Vue({
+    router,
     metaInfo () {
       return {
         title: 'Boring Title',
@@ -156,11 +157,6 @@ export default function createApp () {
     </div>`
   })
 
-  const app = new Vue({
-    router,
-    render: h => h(App)
-  })
-
   const { set } = app.$meta().addApp('custom')
   set({
     bodyAttrs: { class: 'custom-app' },