flatdeb-builder: Use the packaged flatdeb

This also allows us to easily get the changes in v2021-updates.

https://phabricator.apertis.org/T8507



Signed-off-by: Ryan Gonzalez <ryan.gonzalez@collabora.com>

flatdeb-builder/Dockerfile

@@ -19,6 +19,7 @@ ENV DEBIAN_FRONTEND=noninteractive
 ENV TMP="/scratch"
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
+        apertis-flatdeb \
         apt-transport-https \
         bash \
         binfmt-support \
@@ -50,8 +51,8 @@ RUN apt-get update && \
         user-mode-linux \
         udev
 
-# FIXME: move to a packaged version
-RUN git clone --branch apertis/$RELEASE --depth 1 https://gitlab.apertis.org/infrastructure/apertis-flatdeb.git /opt/apertis-flatdeb
+# Create a symlink alias for all the CI jobs that assume this path.
+RUN ln -s /usr/share/flatdeb /opt/apertis-flatdeb
 
 # Defer libnss-unknown package installation to the end to avoid possible UID/GID problems
 RUN apt-get update  && \