`extract_scene.py` calls `main` without argument

[leotrs]

The main function defined in extract_scene.py accepts a required argument. But the last line of extract_scene.py calls main without arguments.

1. This probably means that nobody is calling extract_scene.py as a standalone script (which would trigger the wrong main() call. If this is the case, we should just delete the last two lines.
2. If we want to support using extract_scene.py as a standalone script, we should fix that call and determine what is the appropriate config to be passed to main in that case.

[leotrs]

#98 closes this.