Batocera's cores were read from configgen-defaults.yml, one per system,
and a hand-kept registry list overrode even that; DOSBox Staging,
melonDS DS and nine other cores a user can pick in ES were outside the
pack, while mamemess, which Batocera does not ship, was in. The
scraper now reads es_systems.yml, the registry list is gone, and the
target scraper names standalone emulators (amiberry, fsuae, vice)
instead of only the machines listed under them.