tl;dr - They cannot be deleted: save your new image, delete all the images and load it back
For anyone landing here, please read carefully Docker’s documentation and previous answers: as stated before ‘<none>:<none>’ images are intermediate images created during a build command and are parents of the newly created and, again, cannot be deleted.
docker image prune -f will not delete that images, I’ve personally tested every command mentioned on this post and the only way I’ve found to achieve that is using docker save/load:
docker save --output image.tar ImageID-or-Name
docker image prune -fa
docker load --input image.tar