ci: Drop x86_build_old image

Currently not used for anything.

v2:
* Drop build script as well (Eric Anholt)

Fixes: a3543adc26 "clover: set LLVM min version to 8.0.1"
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7902>

.gitlab-ci.yml

@@ -352,20 +352,6 @@ x86_test-vk:
   variables:
     MESA_IMAGE_TAG: &x86_test-vk "2020-11-06-deqp-version"
 
-# Debian 9 based x86 build image (old LLVM)
-x86_build_old:
-  extends: x86_build-base
-  variables:
-    MESA_IMAGE_TAG: &x86_build_old "2020-12-02"
-    FDO_DISTRIBUTION_VERSION: stretch-slim
-
-.use-x86_build_old:
-  variables:
-    TAG: *x86_build_old
-  image: "$CI_REGISTRY_IMAGE/debian/x86_build_old:${TAG}-${MESA_TEMPLATES_COMMIT}"
-  needs:
-    - x86_build_old
-
 # Debian 10 based ARM build image
 arm_build:
   extends:

.gitlab-ci/container/x86_build_old.sh

@@ -1,69 +0,0 @@
-#!/bin/bash
-
-set -e
-set -o xtrace
-
-export DEBIAN_FRONTEND=noninteractive
-
-apt-get install -y \
-      apt-transport-https \
-      ca-certificates
-
-sed -i -e 's/http:\/\/deb/https:\/\/deb/g' /etc/apt/sources.list
-echo 'deb https://deb.debian.org/debian stretch-backports main' >/etc/apt/sources.list.d/backports.list
-
-apt-get update
-
-# Use newer packages from backports by default
-cat >/etc/apt/preferences <<EOF
-Package: *
-Pin: release a=stretch-backports
-Pin-Priority: 500
-EOF
-
-apt-get dist-upgrade -y
-
-apt-get install -y --no-remove \
-      bison \
-      bzip2 \
-      ccache \
-      flex \
-      g++ \
-      gcc \
-      git \
-      libclang-3.9-dev \
-      libclang-4.0-dev \
-      libclang-5.0-dev \
-      libclang-6.0-dev \
-      libclang-7-dev \
-      libclc-dev \
-      libdrm-dev \
-      libelf-dev \
-      libepoxy-dev \
-      libexpat1-dev \
-      libpng-dev \
-      libunwind-dev \
-      llvm-3.9-dev \
-      llvm-4.0-dev \
-      llvm-5.0-dev \
-      llvm-6.0-dev \
-      llvm-7-dev \
-      ninja-build \
-      pkg-config \
-      python-mako \
-      python3-mako \
-      python3-pip \
-      python3-setuptools \
-      python3-wheel \
-      scons \
-      xz-utils \
-      zlib1g-dev
-
-# We need at least 0.52.0, which is not in stretch
-python3 -m pip install meson>=0.52
-
-. .gitlab-ci/container/container_pre_build.sh
-
-############### Uninstall unused packages
-
-. .gitlab-ci/container/container_post_build.sh