Updates to go-systemd and selinux

caught these when i was looking at cadvisor's deps.

Signed-off-by: Davanum Srinivas <davanum@gmail.com>

vendor/github.com/opencontainers/selinux/go-selinux/label/label_stub.go

@@ -15,10 +15,6 @@ func GenLabels(options string) (string, string, error) {
 	return "", "", nil
 }
 
-func FormatMountLabel(src string, mountLabel string) string {
-	return src
-}
-
 func SetFileLabel(path string, fileLabel string) error {
 	return nil
 }