flatcar-postinst: Remove old Tectonic workaround

The Docker 1.12 version required by old Tectonic clusters is long gone
on Flatcar and the workaround to switch the node to the old Docker won't
work anymore.
Remove the Tectonic workaround.

Author: pothos

flatcar-postinst

@@ -153,101 +153,13 @@ PrivateTmp=true
 EOF
 fi
 
-# Tectonic backed itself into a corner by depending on the docker version
-# shipped in Container Linux but not actively ensuring that they kept clusters
-# up-to-date. As a result, the OS has continued to ship an old docker to work
-# around the issue. Now that Tectonic is able to specify the version of docker,
-# the default version of docker can be updated. Unfortunately, this can't be
-# done until all clusters have fallen out of support or have updated. In order
-# to expedite this process, the /etc/coreos/docker-1.12 flag file has been
-# added, which can signal that the installed version of docker should remain at
-# 1.12.6. This next chunk of black magic attempts to determine if the machine
-# is a part of a Tectonic cluster and, if so, write the flag file so that old
-# clusters aren't caught up in the docker-version bump.
-#
-# This code works by looking at the kubelet.service and a particular sysctl
-# entry that have always been written by the Tectonic installer. After
-# stripping out known variables and commonly-added user modifications, the
-# contents are hashed and compared against a known, good list. This list was
-# derived from every kubelet.service we have ever shipped in Tectonic. This was
-# not a particularly fun exercise.
-good_kubelet() {
-    KUBELET_PATH="/etc/systemd/system/kubelet.service"
-    declare -A GOOD_KUBELET_SUMS=(
-        [9aa254d55054fab5de48ca4e97ac3f0f]=1
-        [838ca6c80119a7daf9fdc3881698d058]=1
-        [35dd901dd87291df1ad8b6bf9b60a174]=1
-        [43af37f891e555c5e4cf7c18478fce54]=1
-        [c27121efdd210cc05a28c122f8f4a145]=1
-        [f4cab5080e349a999197daace5ca971c]=1
-        [71f8b465420d9373a536424eb81987ad]=1
-        [997f455cd2a02ce885e5ec7db4755fa5]=1
-        [69d890f526fe59da3117f56583bc9929]=1
-        [46a19863e5497f903fb3fdc0fbda9137]=1
-        [42357b95fc5ae52b476b8eb5c58ebb42]=1
-        [ee5ef7bb3443f872fe470f4eab586b3c]=1
-        [5b08a40b4f8312c4710b1676b761a9b0]=1
-        [879210fde7b8a3c8c02b8646dd06a35e]=1
-        [b0cf744da1a9b5df933baabdcfb5bf7f]=1
-        [b3c382658e55ada45a819c3274d25cb2]=1
-        [852dd9b686429b84144b36e101305968]=1
-    )
-
-    [ -f $KUBELET_PATH ] || return 1
-
-    # Remove all whitespace (including newlines), backslashes, known variables
-    # (the first six expressions), and commonly-added user options (the next
-    # two expressions) before determining the md5 sum.
-    sum=$(sed \
-        --regexp-extended \
-        --expression '/--cloud-provider=/d' \
-        --expression '/--hostname-override=/d' \
-        --expression '/--cluster-dns=/d' \
-        --expression '/--cluster_dns=/d' \
-        --expression '/--node-labels=/d' \
-        --expression '/--cni-bin-dir=/d' \
-        --expression '/--register-with-taints=/d' \
-        --expression '/\/opt\/s3-puller.sh/d' \
-        --expression '/-v=/d' \
-        --expression '/-vmodule=/d' \
-        --expression 's/\s//g' \
-        --expression 's/\\//g' \
-        $KUBELET_PATH | tr --delete '\n' | md5sum | gawk '{print $1}')
-
-    [[ -n "${GOOD_KUBELET_SUMS[${sum}]}" ]] && return 0
-}
-
-good_sysctl() {
-    SYSCTL_PATH="/etc/sysctl.d/max-user-watches.conf"
-    declare -A GOOD_SYSCTL_SUMS=(
-        [6de69b29eccf652d476f68c1abf3d0db]=1
-        [52ddc3d78f9ce25f068c6da1c1f7f2f3]=1
-    )
-
-    [ -f $SYSCTL_PATH ] || return 1
-
-    sum=$(md5sum $SYSCTL_PATH | gawk '{print $1}')
-
-    [[ -n "${GOOD_SYSCTL_SUMS[${sum}]}" ]] && return 0
-}
-
 # Gather metadata about upcoming OS image.
 # shellcheck source=/dev/null
 source "${INSTALL_MNT}/lib/os-release"
 NEXT_VERSION_ID=${VERSION_ID}
 
-# Check to make sure that the current version is less than 1576 (this is the
-# first release to include this Tectonic work-around). This ensures that we
-# only apply this work-around one time.
 # shellcheck source=/dev/null
 source /usr/lib/os-release
-DOCKER_FLAG_PATH="/etc/flatcar/docker-1.12"
-if [ ! -e "${DOCKER_FLAG_PATH}" ] && [ "${VERSION_ID%%.*}" -lt 1576 ] &&
-    good_kubelet && good_sysctl
-then
-    echo "Detected a Tectonic cluster. Writing docker override..."
-    cat > "${DOCKER_FLAG_PATH}" <<< yes
-fi
 
 tee_journal() {
     tee >(systemd-cat -t coreos-postinst)