Dockerfile.isar: Clean up dependency installation

autoconf, automake, libtool were never official dependencies. Their
addition comes from the early Isar days, likely misunderstanding the
actual needs already back then.

e2fsprogs and multistrap were only needed up to Isar v0.5 from 2018.
It's fair to drop support for these historic versions now.

debhelper was added along sbuild support in 54ab356f9f but never
became an official upstream dependency - drop it again.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

Dockerfile.isar

@@ -9,11 +9,11 @@ ARG DEBIAN_FRONTEND=noninteractive
 ENV LC_ALL=en_US.UTF-8
 RUN apt-get update && \
     apt-get install -y -f --no-install-recommends \
-            autoconf automake gdisk libtool bash-completion \
-            reprepro python3 binfmt-support e2fsprogs \
+            gdisk bash-completion \
+            reprepro python3 binfmt-support \
             umoci skopeo \
-            git-buildpackage pristine-tar schroot sbuild debhelper \
-            multistrap qemu-user-static debootstrap quilt && \
+            git-buildpackage pristine-tar schroot sbuild \
+            qemu-user-static debootstrap quilt && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*