refactor: remove potential double free when managing WebContents (#15280)

* refactor: remove -new-contents-created event

Chromium expects us to take ownership of WebContents in AddNewContents,
we should not create V8 wrapper in WebContentsCreated, otherwise we
would have WebContents being managed by 2 unique_ptr at the same time.

* refactor: make CreateAndTake take unique_ptr

lib/browser/guest-view-manager.js

@@ -157,14 +157,6 @@ const createGuest = function (embedder, params) {
       }
     }
   })
-  guest.on('-web-contents-created', (...args) => {
-    if (guest.getLastWebPreferences().nativeWindowOpen === true) {
-      const embedder = getEmbedder(guestInstanceId)
-      if (embedder != null) {
-        embedder.emit('-web-contents-created', ...args)
-      }
-    }
-  })
 
   return guestInstanceId
 }