remove duplicate definition of org-ditaa-jar-path

* lisp/ob-ditaa.el (org-ditaa-jar-path): Already defined in
  org-exp-blocks.el.
* lisp/org-exp-blocks.el (org-ditaa-jar-path): Declare appropriately
  for the fact that this is really now a Babel thing -- even if it is
  used here and the definition should remain here for reasons of load
  dependencies.

lisp/ob-ditaa.el

@@ -37,6 +37,7 @@
 
 ;;; Code:
 (require 'ob)
+(require 'org-exp-blocks)
 
 (defvar org-babel-default-header-args:ditaa
   '((:results . "file")
@@ -44,11 +45,6 @@
     (:java . "-Dfile.encoding=UTF-8"))
   "Default arguments for evaluating a ditaa source block.")
 
-(defcustom org-ditaa-jar-path nil
-  "Path for the ditaa jar file."
-  :group 'org-babel
-  :type 'string)
-
 (defcustom org-ditaa-jar-option "-jar"
   "Option for the ditaa jar file.
 Do not leave leading or trailing spaces in this string."

lisp/org-exp-blocks.el

@@ -225,7 +225,7 @@ which defaults to the value of `org-export-blocks-witheld'."
 
 ;;--------------------------------------------------------------------------------
 ;; ditaa: create images from ASCII art using the ditaa utility
-(defvar org-ditaa-jar-path (expand-file-name
+(defcustom org-ditaa-jar-path (expand-file-name
 			    "ditaa.jar"
 			    (file-name-as-directory
 			     (expand-file-name
@@ -234,7 +234,9 @@ which defaults to the value of `org-export-blocks-witheld'."
 			       (expand-file-name
 				"../contrib"
 				(file-name-directory (or load-file-name buffer-file-name)))))))
-  "Path to the ditaa jar executable.")
+  "Path to the ditaa jar executable."
+  :group 'org-babel
+  :type 'string)
 
 (defvar org-export-current-backend) ; dynamically bound in org-exp.el
 (defun org-export-blocks-format-ditaa (body &rest headers)