Containerfile: clean up temporary hack for `--from` handling

We have new enough rpm-ostree in Fedora for this now.

Containerfile

@@ -39,17 +39,12 @@ COPY . /src
 WORKDIR /src
 RUN rm -vf /src/*.repo
 COPY --from=repos /etc/yum.repos.d/*.repo /src
-# Brutally inject releasever and repos into manifest file. This is a major hack
-# until rpm-ostree does this on its own: https://github.com/coreos/rpm-ostree/pull/5136
-RUN --mount=type=bind,from=repos,src=/,dst=/repos source /repos/etc/os-release && \
- echo -e "\nreleasever: $VERSION_ID" >> ${MANIFEST} && \
- echo -e "\nrepos:\n" >> ${MANIFEST} && \
- dnf repolist --setopt=reposdir=. | tail -n +2 | cut -f1 -d' ' | sed 's/^/- /' >> ${MANIFEST}
 RUN --mount=type=cache,target=/workdir \
     --mount=type=bind,rw=true,src=.,dst=/buildcontext,bind-propagation=shared \
+    --mount=type=bind,from=repos,src=/,dst=/repos \
       rpm-ostree compose image --image-config fedora-bootc-config.json \
         --cachedir=/workdir --format=ociarchive --initialize ${MANIFEST} \
-        /buildcontext/out.ociarchive
+       --source-root=/repos /buildcontext/out.ociarchive
 
 FROM oci-archive:./out.ociarchive
 # Need to reference builder here to force ordering. But since we have to run