Create a buffet world (type floating island) with generate structures OFF
edit level.dat to make it a void world with vanilla biomes (generatorOptions > biome_source: type: minecraft:vanilla_layered // chunk_generator: > options: default_block: minecraft:air + default_fluid: minecraft:air)
delete "region" folder in saves
As seen on the screenshot there are still bone fossils and it seems there is no way to disable them
This may have been fixed along with MC-171491. Is this still an issue for you?