Install ros_gz from package, not from source, remove from .repos

Author: amarburg

.docker/Dockerfile

@@ -128,6 +128,7 @@ RUN wget https://packages.osrfoundation.org/gazebo.gpg -O /usr/share/keyrings/pk
     && apt-get -q update \
     && apt-get -y --quiet --no-install-recommends install \
     gz-${GZ_VERSION} \
+    ros-${ROS_DISTRO}-ros-gz${GZ_VERSION} \
     && apt-get autoremove -y \
     && apt-get clean -y \
     && rm -rf /var/lib/apt/lists/*