ox-texinfo: Do not hardcode "Manual" in top node

* lisp/ox-texinfo.el (org-texinfo-template): Do not hardcode "Manual"
  in top node.

lisp/ox-texinfo.el

@@ -804,7 +804,7 @@ holding export options."
      ;; Configure Top Node when not for Tex
      "@ifnottex\n"
      "@node Top\n"
-     "@top " title " Manual\n"
+     (format "@top %s\n" title)
      (and copying "@insertcopying\n")
      "@end ifnottex\n\n"
      ;; Menu.