boot0: Drop the BOOT_BOOT0_ORG option.

This shouldn't be an option (and I added it in the first place back in
4ae4202e705cf6a12aa3cbb49efb153879a6bc2f and
83f4b92050cbf8913d5c0aac16726c783d8b2d9c). However, unlike the other
knobs I added back then, this really shouldn't be a knob since it is
hardcoded in the source.