ci: remove the emulated aarch64-gnu image

src/ci/docker/host-x86_64/disabled/aarch64-gnu/Dockerfile

@@ -1,79 +0,0 @@
-FROM ubuntu:16.04
-
-RUN apt-get update -y && apt-get install -y --no-install-recommends \
-      bc \
-      bzip2 \
-      ca-certificates \
-      cmake \
-      cpio \
-      curl \
-      file \
-      g++ \
-      gcc-aarch64-linux-gnu \
-      git \
-      libc6-dev \
-      libc6-dev-arm64-cross \
-      make \
-      python3 \
-      qemu-system-aarch64 \
-      xz-utils
-
-ENV ARCH=arm64 \
-    CROSS_COMPILE=aarch64-linux-gnu-
-
-WORKDIR /build
-
-# Compile the kernel that we're going to run and be emulating with. This is
-# basically just done to be compatible with the QEMU target that we're going
-# to be using when running tests. If any other kernel works or if any
-# other QEMU target works with some other stock kernel, we can use that too!
-#
-# The `config` config file was a previously generated config file for
-# the kernel. This file was generated by running `make defconfig`
-# followed by `make menuconfig` and then enabling the IPv6 protocol page.
-COPY host-x86_64/aarch64-gnu/config /build/.config
-RUN curl https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.4.42.tar.xz | \
-      tar xJf - && \
-      cd /build/linux-4.4.42 && \
-      cp /build/.config . && \
-      make -j$(nproc) all && \
-      cp arch/arm64/boot/Image /tmp && \
-      cd /build &&  \
-      rm -rf linux-4.4.42
-
-# Compile an instance of busybox as this provides a lightweight system and init
-# binary which we will boot into. Only trick here is configuring busybox to
-# build static binaries.
-RUN curl https://www.busybox.net/downloads/busybox-1.21.1.tar.bz2 | tar xjf - && \
-      cd busybox-1.21.1 && \
-      make defconfig && \
-      sed -i 's/.*CONFIG_STATIC.*/CONFIG_STATIC=y/' .config && \
-      make -j$(nproc) && \
-      make install && \
-      mv _install /tmp/rootfs && \
-      cd /build && \
-      rm -rf busybox-1.12.1
-
-# Download the ubuntu rootfs, which we'll use as a chroot for all our tests.
-WORKDIR /tmp
-RUN mkdir rootfs/ubuntu
-RUN curl http://cdimage.ubuntu.com/ubuntu-base/releases/16.04/release/ubuntu-base-16.04-core-arm64.tar.gz | \
-      tar xzf - -C rootfs/ubuntu && \
-      cd rootfs && mkdir proc sys dev etc etc/init.d
-
-# Copy over our init script, which starts up our test server and also a few
-# other misc tasks.
-COPY scripts/qemu-bare-bones-rcS rootfs/etc/init.d/rcS
-RUN chmod +x rootfs/etc/init.d/rcS
-
-# Helper to quickly fill the entropy pool in the kernel.
-COPY scripts/qemu-bare-bones-addentropy.c /tmp/addentropy.c
-RUN aarch64-linux-gnu-gcc addentropy.c -o rootfs/addentropy -static
-
-COPY scripts/sccache.sh /scripts/
-RUN sh /scripts/sccache.sh
-
-ENV RUST_CONFIGURE_ARGS \
-      --qemu-aarch64-rootfs=/tmp/rootfs
-ENV SCRIPT python3 ../x.py test --target aarch64-unknown-linux-gnu
-ENV NO_CHANGE_USER=1