ci: drop CentOS 6

CentOS 6 is no longer supported by upstream so we cannot test against it
for future Xen releases.

Signed-off-by: Doug Goldstein <cardoe@cardoe.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

automation/build/centos/6.dockerfile

@@ -1,51 +0,0 @@
-FROM centos:6
-LABEL maintainer.name="The Xen Project" \
-      maintainer.email="xen-devel@lists.xenproject.org"
-
-RUN mkdir /build
-WORKDIR /build
-
-# work around https://github.com/moby/moby/issues/10180
-# and add EPEL for dev86
-RUN rpm --rebuilddb && \
-    yum -y install \
-        yum-plugin-ovl \
-        epel-release \
-    && yum clean all && \
-    rm -rf /var/cache/yum
-
-# install Xen depends
-RUN yum -y install \
-        gcc \
-        gcc-c++ \
-        ncurses-devel \
-        zlib-devel \
-        openssl-devel \
-        python-devel \
-        libuuid-devel \
-        pciutils-devel \
-        pkgconfig \
-        gettext \
-        flex \
-        bison \
-        libaio-devel \
-        glib2-devel \
-        yajl-devel \
-        pixman-devel \
-        glibc-devel \
-        glibc-devel.i686 \
-        make \
-        binutils \
-        git \
-        wget \
-        acpica-tools \
-        python-markdown \
-        patch \
-        checkpolicy \
-        dev86 \
-        iasl \
-        xz-devel \
-        bzip2 \
-        nasm \
-    && yum clean all && \
-    rm -rf /var/cache/yum

automation/gitlab-ci/build.yaml

@@ -176,16 +176,6 @@ centos-7-gcc-debug:
   variables:
     CONTAINER: centos:7
 
-centos-6-gcc:
-  extends: .gcc-x86-64-build
-  variables:
-    CONTAINER: centos:6
-
-centos-6-gcc-debug:
-  extends: .gcc-x86-64-build-debug
-  variables:
-    CONTAINER: centos:6
-
 debian-jessie-clang:
   extends: .clang-x86-64-build
   variables:

automation/scripts/containerize

@@ -25,7 +25,6 @@ die() {
 BASE="registry.gitlab.com/xen-project/xen"
 case "_${CONTAINER}" in
     _archlinux|_arch) CONTAINER="${BASE}/archlinux:current" ;;
-    _centos6) CONTAINER="${BASE}/centos:6" ;;
     _centos7) CONTAINER="${BASE}/centos:7" ;;
     _centos72) CONTAINER="${BASE}/centos:7.2" ;;
     _fedora) CONTAINER="${BASE}/fedora:29";;