revert: "fix: window.open site instance should belong to same browsing instance (#15216)" (#15757)

This reverts commit 8f35198bfb.

spec/fixtures/api/sandbox.html

@@ -81,9 +81,6 @@
       },
       'window-open-external': () => {
         addEventListener('load', () => {
-          ipcRenderer.once('open-the-popup', (event, url) => {
-            popup = open(url, '', 'top=65,left=55,width=505,height=605')
-          })
           ipcRenderer.once('touch-the-popup', () => {
             let errorMessage = null
             try {
@@ -93,7 +90,7 @@
             }
             ipcRenderer.send('answer', errorMessage)
           })
-          ipcRenderer.send('opener-loaded')
+          popup = open('http://www.google.com/#q=electron', '', 'top=65,left=55,width=505,height=605')
         })
       },
       'verify-ipc-sender': () => {