Remove unnecessary line

Signed-off-by: Daehyeok Mun <daehyeok@gmail.com>

plugin/backend_linux.go

@@ -262,11 +262,9 @@ func (pm *Manager) Upgrade(ctx context.Context, ref reference.Named, name string
 	defer pm.muGC.RUnlock()
 
 	// revalidate because Pull is public
-	nameref, err := reference.ParseNormalizedNamed(name)
-	if err != nil {
+	if _, err := reference.ParseNormalizedNamed(name); err != nil {
 		return errors.Wrapf(err, "failed to parse %q", name)
 	}
-	name = reference.FamiliarString(reference.TagNameOnly(nameref))
 
 	tmpRootFSDir, err := ioutil.TempDir(pm.tmpDir(), ".rootfs")
 	if err != nil {