babel: screen: New variable assignment and expansion scheme

	* ob-screen.el (org-babel-execute:screen): Use generic
	expansion function
	(org-babel-expand-body:screen): Delete function
	(org-babel-prep-session:screen): Remove references to
	processed params

lisp/ob-screen.el

@@ -45,9 +45,6 @@ In case you want to use a different screen than one selected by your $PATH")
   '((:results . "silent") (:session . "default") (:cmd . "sh") (:terminal . "xterm"))
   "Default arguments to use when running screen source blocks.")
 
-(defun org-babel-expand-body:screen (body params)
-  "Expand BODY according to PARAMS, return the expanded body." body)
-
 (defun org-babel-execute:screen (body params)
   "Send a block of code via screen to a terminal using Babel.
 \"default\" session is used when none is specified."
@@ -58,15 +55,13 @@ In case you want to use a different screen than one selected by your $PATH")
            (socket (org-babel-screen-session-socketname session)))
       (unless socket (org-babel-prep-session:screen session params))
       (org-babel-screen-session-execute-string
-       session (org-babel-expand-body:screen body params)))))
+       session (org-babel-expand-body:generic body params)))))
 
 (defun org-babel-prep-session:screen (session params)
   "Prepare SESSION according to the header arguments specified in PARAMS."
   (let* ((processed-params (org-babel-process-params params))
          (session (nth 0 processed-params))
-         (vars (nth 1 processed-params))
          (socket (org-babel-screen-session-socketname session))
-         (vars (org-babel-ref-variables params))
          (cmd (cdr (assoc :cmd params)))
          (terminal (cdr (assoc :terminal params)))
          (process-name (concat "org-babel: terminal (" session ")")))