ci: Slim down lint image

Currently, the lint_test_runner is built and installed into the lint CI
image. This is problematic, because it triggers a full image build on
every change to its source code. Doing a build of the lint test_runner
on every run is easier and faster.

ci/lint_imagefile

@@ -13,7 +13,6 @@ COPY ./ci/retry/retry /ci_retry
 COPY ./.python-version /.python-version
 COPY ./ci/lint/container-entrypoint.sh /entrypoint.sh
 COPY ./ci/lint/04_install.sh /install.sh
-COPY ./test/lint/test_runner /test/lint/test_runner
 
 RUN /install.sh && \
   echo 'alias lint="./ci/lint/06_script.sh"' >> ~/.bashrc && \