ob-comint.el: Reinstate let-bound variable from last commit.

* ob-comint.el (org-babel-comint-eval-invisibly-and-wait-for-file):
  Reinstate `let (v)' which `org-babel-evaluate-session' relies on.

lisp/ob-comint.el

@@ -151,8 +151,10 @@ FILE exists at end of evaluation."
    (if (= (aref string (1- (length string))) ?\n) string (concat string "\n")))
   ;; From Tramp 2.1.19 the following cache flush is not necessary
   (if (file-remote-p default-directory)
-      (with-parsed-tramp-file-name default-directory nil
-	(tramp-flush-directory-property v "")))
+      (let (v)
+	(ignore v)
+	(with-parsed-tramp-file-name default-directory nil
+	  (tramp-flush-directory-property v ""))))
   (while (not (file-exists-p file)) (sit-for (or period 0.25))))
 
 (provide 'ob-comint)