supermin-init-prelude: skip creating cache dir

In a cosa workdir, that dir always exists in both privileged and
unprivileged paths.

Prep for a new command that'll use this code outside a cosa workdir
where to be nice we don't want to just randomly create a cache dir even
when no caching is required.

src/supermin-init-prelude.sh

@@ -47,7 +47,6 @@ for maybe_symlink in "${workdir}"/{src/config,src/yumrepos}; do
     fi
 done
 
-mkdir -p "${workdir}"/cache
 cachedev=$(blkid -lt LABEL=cosa-cache -o device || true)
 if [ -n "${cachedev}" ]; then
     mount "${cachedev}" "${workdir}"/cache