libpod: rm some unused freebsd code

This fixes a bunch of "unused" linter warnings on freebsd.

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

libpod/util_freebsd.go

@@ -3,26 +3,12 @@
 package libpod
 
 import (
-	"errors"
 	"syscall"
 
-	spec "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
 )
 
-// systemdSliceFromPath makes a new systemd slice under the given parent with
-// the given name.
-// The parent must be a slice. The name must NOT include ".slice"
-func systemdSliceFromPath(parent, name string, resources *spec.LinuxResources) (string, error) {
-	return "", errors.New("not implemented systemdSliceFromPath")
-}
-
-// deleteSystemdCgroup deletes the systemd cgroup at the given location
-func deleteSystemdCgroup(path string, resources *spec.LinuxResources) error {
-	return nil
-}
-
 // No equivalent on FreeBSD?
 func LabelVolumePath(path, mountLabel string) error {
 	return nil