libct/utils: stripRoot: rm useless HasPrefix

Using strings.HasPrefix with strings.TrimPrefix results in doing the
same thing (checking if prefix exists) twice. In this case, using
strings.TrimPrefix right away is sufficient.

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

libcontainer/utils/utils.go

@@ -77,7 +77,7 @@ func stripRoot(root, path string) string {
 		path = "/"
 	case root == "/":
 		// do nothing
-	case strings.HasPrefix(path, root+"/"):
+	default:
 		path = strings.TrimPrefix(path, root+"/")
 	}
 	return CleanPath("/" + path)