build: Remove the Gentoo packaging target.

The current target is not functional; the Gentoo packaging is
community maintained anyway.

Change-Id: I7dfe8641ccddb53ff1a448f2afaacaa591fc7dec

docker/Dockerfile_gentoo

-FROM gentoo/stage3-amd64:latest
-
-RUN emerge-webrsync
-
-ADD scripts/gentoo/portage/ /etc/portage/
-
-# profile with gnome and systemd configuration
-RUN eselect profile set 5 && \
-	emerge -uDN world
-
-RUN eselect news read
-
-RUN emerge layman && echo "source /var/lib/layman/make.conf" >> /etc/portage/make.conf
-
-ADD scripts/build-package-gentoo.sh /opt/build-package-gentoo.sh
-
-CMD /bin/bash /opt/build-package-gentoo.sh
-

scripts/make-packaging-target.py

@@ -395,12 +395,6 @@ def run_generate_all(parsed_args):
             "output_file": ".packages-built",
             "options": "--security-opt seccomp=./docker/profile-seccomp-fedora_28.json --privileged"
         },
-        # Gentoo
-        {
-            "distribution": "gentoo",
-            "debian_packaging_override": "",
-            "output_file": ".packages-built",
-        },
         # Snap
         {
             "distribution": "snap",