cmdlib.sh: drop runvm_with_cache_snapshot()

This is now no longer used. runvm_with_cache_snapshot was used by
runvm-osbuild previously but it's not needed any longer and
cosa supermin-run --snapshot was used by build-podman-os job
in the pipeline, but that isn't being used either so we can drop
it.

src/cmd-supermin-run

@@ -6,7 +6,7 @@ dn=$(dirname "$0")
 . "${dn}"/cmdlib.sh
 
 print_help() {
-    echo "Usage: cosa supermin-run [--cache|--snapshot] COMMAND [ARG...]" >&2
+    echo "Usage: cosa supermin-run [--cache] COMMAND [ARG...]" >&2
 }
 
 if [ $# = 0 ]; then
@@ -21,11 +21,6 @@ case "$1" in
         set -- runvm_with_cache -- "$@"
         need_cache_dir=1
         ;;
-    --snapshot)
-        shift
-        set -- runvm_with_cache_snapshot on -- "$@"
-        need_cache_dir=1
-        ;;
     --*)
         echo "unrecognized option: $1"
         print_help

src/cmdlib.sh

@@ -574,10 +574,8 @@ runcompose_tree() {
     fi
 }
 
-# Run with cache disk with optional snapshot=on, which means no changes get written back to
-# the cache disk. `runvm_with_cache_snapshot on` will set snapshotting to on.
-runvm_with_cache_snapshot() {
-    local snapshot=$1; shift
+# Run with cache disk.
+runvm_with_cache() {
     local cache_size=${RUNVM_CACHE_SIZE:-30G}
     # "cache2" has an explicit label so we can find it in qemu easily
     if [ ! -f "${workdir}"/cache/cache2.qcow2 ]; then
@@ -590,16 +588,11 @@ runvm_with_cache_snapshot() {
     fi
     # And remove the old one
     rm -vf "${workdir}"/cache/cache.qcow2
-    cache_args+=("-drive" "if=none,id=cache,discard=unmap,snapshot=${snapshot},file=${workdir}/cache/cache2.qcow2" \
+    cache_args+=("-drive" "if=none,id=cache,discard=unmap,file=${workdir}/cache/cache2.qcow2" \
                         "-device" "virtio-blk,drive=cache")
     runvm "${cache_args[@]}" "$@"
 }
 
-runvm_with_cache() {
-    local snapshot='off'
-    runvm_with_cache_snapshot $snapshot "$@"
-}
-
 # Strips out the digest field from lockfiles since they subtly conflict with
 # various workflows.
 strip_out_lockfile_digests() {