CI Cleanup: Remove cgroups v1 support

With (esp. Debian) CI VM images built by
https://github.com/containers/automation_images/ pull/338 CI no-longer
tests with runc nor cgroups v1.  Add logic to fail under these
conditions.  Prune back high-level YAML/script envars and logic formerly
required to support these things.

Signed-off-by: Chris Evich <cevich@redhat.com>

contrib/cirrus/lib.sh

@@ -94,7 +94,7 @@ EPOCH_TEST_COMMIT="$CIRRUS_BASE_SHA"
 # are consumed by the passthrough_envars() automation library function.
 #
 # List of envariables which must be EXACT matches
-PASSTHROUGH_ENV_EXACT='CGROUP_MANAGER|DEST_BRANCH|DISTRO_NV|GOCACHE|GOPATH|GOSRC|NETWORK_BACKEND|OCI_RUNTIME|PODMAN_IGNORE_CGROUPSV1_WARNING|ROOTLESS_USER|SCRIPT_BASE|SKIP_USERNS|EC2_INST_TYPE|PODMAN_DB|STORAGE_FS|PODMAN_BATS_LEAK_CHECK'
+PASSTHROUGH_ENV_EXACT='CGROUP_MANAGER|DEST_BRANCH|DISTRO_NV|GOCACHE|GOPATH|GOSRC|NETWORK_BACKEND|OCI_RUNTIME|ROOTLESS_USER|SCRIPT_BASE|SKIP_USERNS|EC2_INST_TYPE|PODMAN_DB|STORAGE_FS|PODMAN_BATS_LEAK_CHECK'
 
 # List of envariable patterns which must match AT THE BEGINNING of the name.
 # Consumed by the passthrough_envars() automation library function.

contrib/cirrus/logcollector.sh

@@ -46,7 +46,6 @@ case $1 in
                     netavark
                     passt
                     podman
-                    runc
                     skopeo
                     slirp4netns
         )

contrib/cirrus/setup_environment.sh

@@ -74,24 +74,9 @@ cd "${GOSRC}/"
 
 mkdir -p /etc/containers/containers.conf.d
 
-# Defined by lib.sh: Does the host support cgroups v1 or v2? Use runc or crun
-# respectively.
-# **IMPORTANT**: $OCI_RUNTIME is a fakeout! It is used only in e2e tests.
-# For actual podman, as in system tests, we force runtime in containers.conf
-showrun echo "conditional check: CG_FS_TYPE [=$CG_FS_TYPE]"
-case "$CG_FS_TYPE" in
-    tmpfs)
-        if ((CONTAINER==0)); then
-            warn "Forcing testing with runc instead of crun"
-            echo "OCI_RUNTIME=runc" >> /etc/ci_environment
-            printf "[engine]\nruntime=\"runc\"\n" > /etc/containers/containers.conf.d/90-runtime.conf
-        fi
-        ;;
-    cgroup2fs)
-        # Nothing to do: podman defaults to crun
-        ;;
-    *) die_unknown CG_FS_TYPE
-esac
+# Only cgroups v2 is supported, die if anything else.
+[[ "$CG_FS_TYPE" == "cgroup2fs" ]] || \
+    die "Only cgroups v2 CI VMs are supported, not: '$CG_FS_TYPE'"
 
 # For testing boltdb without having to use --db-backend.
 # As of #20318 (2023-10-10) sqlite is the default, so do not create
@@ -132,12 +117,7 @@ fi
 # Which distribution are we testing on.
 case "$OS_RELEASE_ID" in
     debian)
-        showrun echo "more conditional setup for debian"
-        # FIXME 2023-04-11: workaround for runc regression causing failure
-        # in system tests: "skipping device /dev/char/10:200 for systemd"
-        # (Checked on 2023-08-08 and it's still too old: 1.1.5)
-        # FIXME: please remove this once runc >= 1.2 makes it into debian.
-        showrun modprobe tun
+        showrun echo "No-op conditional setup for debian"
         ;;
     fedora)
         showrun echo "conditional setup for fedora"
@@ -202,6 +182,7 @@ showrun echo "about to set up for TEST_ENVIRON [=$TEST_ENVIRON]"
 case "$TEST_ENVIRON" in
     host)
         # The e2e tests wrongly guess `--cgroup-manager` option
+        # under some runtime contexts like rootless.
         # shellcheck disable=SC2154
         if [[ "$CG_FS_TYPE" == "cgroup2fs" ]] || [[ "$PRIV_NAME" == "root" ]]
         then