nuke d8/d16 configs for 4mb/8mb setups. only have 2mb and 16mb configs

4mb and 8mb users can just pad their roms to 16mb, using the instructions on
<https://libreboot.org/faq.html#how-do-i-pad-a-rom-before-flashing>

maintaining them in lbmk is a waste of time, and also a hazard because it's a
lot of duplicated labour when making any changes, which could result in awful
mistakes being made