feat(external-api) drop iframe sandbox

It has created more trouble than it sat to solve, I'm dropping it for
now so we can re-evaluate.

modules/API/external/external_api.js

@@ -393,14 +393,6 @@ export default class JitsiMeetExternalAPI extends EventEmitter {
         this._frame.name = frameName;
         this._frame.id = frameName;
         this._setSize(height, width);
-        this._frame.sandbox = [
-            'allow-scripts',
-            'allow-same-origin',
-            'allow-popups',
-            'allow-forms',
-            'allow-downloads',
-            'allow-top-navigation-by-user-activation'
-        ].join(' ');
         this._frame.setAttribute('allowFullScreen', 'true');
         this._frame.style.border = 0;