org.texi: Replace broken example script for batch execution

* doc/org.texi: Example bash script to tangle from *.org file was broken
and obsolete; fixed to now work with recent versions of Org.

There is an example bash script in section  14.12 of the Org manual which
is meant to tangle source blocks from a supplied list of Org files.

The present version is broken in several small ways (it appears to date
from a period when babel was still part of contrib), and requires a
hard-coded specification of the path ORG_HOME.

I've fixed the issue with ORG_HOME, another issue with grepping for strings
that no longer are emitted by ob-tangle, and removed some obsolete
dependencies.

I'm finding the corrected script a useful thing to call from makefiles.

doc/org.texi

@@ -16839,13 +16839,11 @@ done
 
 emacs -Q --batch \
      --eval "(progn
-(add-to-list 'load-path (expand-file-name \"~/src/org/lisp/\"))
-(add-to-list 'load-path (expand-file-name \"~/src/org/contrib/lisp/\" t))
-(require 'org)(require 'org-exp)(require 'ob)(require 'ob-tangle)
+     (require 'org)(require 'ob)(require 'ob-tangle)
      (mapc (lambda (file)
             (find-file (expand-file-name file \"$DIR\"))
             (org-babel-tangle)
-       (kill-buffer)) '($FILES)))" 2>&1 |grep tangled
+            (kill-buffer)) '($FILES)))" 2>&1 |grep -i tangled
 @end example
 
 @node Miscellaneous