Exported Builder scenes have outdated data

When I export a scene from the Builder, the scene.json is full of very outdated fields that cause issues and confusion when trying to run with the SDK.

See the scene.json in this example, that I exported from the Builder:
[Dry_river.zip](https://github.com/decentraland/builder/files/8224357/Dry_river.zip)

It includes the following sections, that shouldn't be there:

- communications
- policy
- source

The source section maybe can stay there, but we should really really remove the "rotation" tag inside the "soruce" section. This tag is misleading, as it's not used outside the Builder. Almost every week somebody in Discord asks why changing the rotation there doesn't work.

It would really help if the scene.json also included the following missing sections:

- spawnPoints
- requiredPermissions
- featureToggles
- description (inside the "display" section)

It would be ideal to copy the default scene.json that the CLI generates:

```json
{
"display": {
"title": "DCL Scene",
"description": "My new Decentraland project",
"navmapThumbnail": "images/scene-thumbnail.png",
"favicon": "favicon_asset"
},
"owner": "",
"contact": {
"name": "author-name",
"email": ""
},
"main": "bin/game.js",
"tags": [],
"scene": {
"parcels": ["0,0"],
"base": "0,0"
},
"spawnPoints": [
{
"name": "spawn1",
"default": true,
"position": {
"x": 0,
"y": 0,
"z": 0
},
"cameraTarget": {
"x": 8,
"y": 1,
"z": 8
}
}
],
"requiredPermissions": [
"ALLOW_TO_MOVE_PLAYER_INSIDE_SCENE"
],
"featureToggles": {}
}
```