Tileset info request should not return the `datafile` field

```
{
"datafile": "http://localhost:8989/api/v1/tilesets/media/uploads/bedpe_mOTjjJ2.db",
"name": "bedpe.db",
"server": "http://localhost:8989/api/v1",
"tilesetUid": "cVy8NEbxSoijEqpH0XnK-g",
"uid": "E0tHFp2UTJ6IkSLlVyWrnQ",
"type": "horizontal-2d-rectangle-domains",
"options": {
"labelColor": "black",
"labelPosition": "hidden",
"name": "bedpe.db"
},
"width": 908,
"height": 178,
"position": "top"
}
```

Probably related to this line in `higlass_server`:

```
#ts_serializer = tss.UserFacingTilesetSerializer(queryset, many=True)
page = self.paginate_queryset(queryset)
if page is not None:
serializer = self.get_serializer(page, many=True)
return self.get_paginated_response(serializer.data)
```