ob-lob: Remove `org-babel-lob-files'

* lisp/ob-lob.el (org-babel-lob-files): Remove variable.
(org-babel-library-of-babel): Fix docstring.

Since its creation, `org-babel-lob-files' has been a no-op.  Since no-one
noticed it during those 7 years, it can safely be removed.

Reported-by: "Charles C. Berry" <ccberry@ucsd.edu>
<http://permalink.gmane.org/gmane.emacs.orgmode/107824>

lisp/ob-lob.el

@@ -35,15 +35,8 @@
 
 (defvar org-babel-library-of-babel nil
   "Library of source-code blocks.
-This is an association list.  Populate the library by adding
-files to `org-babel-lob-files'.")
-
-(defcustom org-babel-lob-files nil
-  "Files used to populate the `org-babel-library-of-babel'.
-To add files to this list use the `org-babel-lob-ingest' command."
-  :group 'org-babel
-  :version "24.1"
-  :type '(repeat file))
+This is an association list.  Populate the library by calling
+`org-babel-lob-ingest' on files containing source blocks.")
 
 (defvar org-babel-default-lob-header-args
   '((:cache . "no")