vendor: bump runc to v1.2.1

For one thing, this release decouples device management from
libcontainer/cgroups. You can see the result of this in a dropped
cilium/ebpf dependency (which is only needed for device management).

NOTE that due to an issue with go mod / go list,
github.com/opencontainers/runc had to be added to
hack/unwanted-dependencies.json under x/exp. This is bogus because
opencontainers/runc does not use x/exp directly, only via cilium/ebpf
dependency (which is not vendored here).

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

vendor/github.com/opencontainers/runc/libcontainer/cgroups/fs2/defaultpath.go

@@ -55,6 +55,9 @@ func _defaultDirPath(root, cgPath, cgParent, cgName string) (string, error) {
 		return filepath.Join(root, innerPath), nil
 	}
 
+	// we don't need to use /proc/thread-self here because runc always runs
+	// with every thread in the same cgroup. This lets us avoid having to do
+	// runtime.LockOSThread.
 	ownCgroup, err := parseCgroupFile("/proc/self/cgroup")
 	if err != nil {
 		return "", err