Update the frozen images to also be based on Debian bullseye. Using the "slim"
variant (which looks to have all we're currently using), and remove the
buildpack-dep frozen image.
The buildpack-dep image is quite large, and it looks like we only use it to
compile some C binaries, which should work fine on a regular debian image;
docker build -t debian:bullseye-slim-gcc -<<EOF
FROM debian:bullseye-slim
RUN apt-get update && apt-get install -y gcc libc6-dev --no-install-recommends
EOF
docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
debian bullseye-slim-gcc 1851750242af About a minute ago 255MB
buildpack-deps bullseye fe8fece98de2 2 days ago 834MB
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>