python 3 is default now, in all the distros

specifically calling "python3" often doesn't work anymore

python2 is obsolete

let python2 die

previously, "normal" initmode relied on the vgarom-based
seabios config, which enables option roms, but then lbmk
would insert pci-optionrom-exec 0 for vgarom, and 2 for normal

in libreboot, coreboot roms with "vgarom" in the filename do
pci option rom execution from coreboot, and "normal" roms
do execution from seabios(where seabios is the only payload
provided on normal setups)

this is because payloads like grub can also be used, on vgarom
setups, where coreboot must handle oprom execution

with this change, it's unlikely we'll hit errors again. previously,
some projects used were calling "python" which in context was
python3, but on some setups, the user only has python2 and python3
but no symlink for "python" (which if exists, we assumed linked to
python3)

now it's unambiguous. docs/build/ can probably be updated now, as
a result of this change, to remove the advice about that

this is forked from the "libre" branch in osboot, which is itself a libre,
deblobbed fork of osboot, a blobbed up fork of libreboot

libreboot needed to be purged clean. this is the new libreboot development
repository. the old one has been abandoned