set default emacs-lisp header args to nil

  The difference between elisp and every other language was causing
  confusion, so simpler just to set these to nil.

* lisp/ob-emacs-lisp.el (org-babel-default-header-args:emacs-lisp):
  Set to nil.

lisp/ob-emacs-lisp.el

@@ -28,8 +28,7 @@
 ;;; Code:
 (require 'ob)
 
-(defvar org-babel-default-header-args:emacs-lisp
-  '((:hlines . "yes") (:colnames . "no"))
+(defvar org-babel-default-header-args:emacs-lisp nil
   "Default arguments for evaluating an emacs-lisp source block.")
 
 (declare-function orgtbl-to-generic "org-table" (table params))