Move dockerhub image to prebuilt z3 (#3714)

Previously, this step was building an incorrect version of Z3 from
source when building the K dockerhub images at release time; this PR
amends the relevant Dockerfile to instead pull from our new prebuilt
images.

I have tested the changes in a reverted commit, as they only run on
release normally. See [this CI
run](https://github.com/runtimeverification/k/actions/runs/6510755942/job/17685127208)
for a successful build of the image using the prebuilt layer.

This PR also removes dead code (`package/debian/Dockerfile`), which as
far as I can tell is not used anywhere any more.

Fixes #3713

package/docker/Dockerfile.ubuntu-jammy

@@ -1,4 +1,4 @@
-FROM ubuntu:jammy
+FROM runtimeverificationinc/z3:ubuntu-jammy-4.12.1
 
 ENV TZ=America/Chicago
 RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
@@ -11,15 +11,6 @@ RUN    apt-get update                   \
                         python3         \
                         python3-pip
 
-RUN    git clone 'https://github.com/z3prover/z3' --branch=z3-4.8.15 \
-    && cd z3                                                         \
-    && python3 scripts/mk_make.py                                    \
-    && cd build                                                      \
-    && make -j8                                                      \
-    && make install                                                  \
-    && cd ../..                                                      \
-    && rm -rf z3
-
 COPY kframework_amd64_ubuntu_jammy.deb /kframework_amd64_ubuntu_jammy.deb
 RUN    apt-get update                                                                   \
     && apt-get upgrade --yes                                                            \