Move org-refile configuration to own block

This fixes a few build warnings concerning undefined variables.

user/emacs.nix

@@ -868,15 +868,6 @@ in
 
           (setq org-tag-alist rah-org-tag-alist)
 
-          ;; Refiling should include not only the current org buffer but
-          ;; also the standard org files. Further, set up the refiling to
-          ;; be convenient with IDO. Follows norang's setup quite closely.
-          (setq org-refile-targets '((nil :maxlevel . 2)
-                                     (org-agenda-files :maxlevel . 2))
-                org-refile-use-outline-path t
-                org-outline-path-complete-in-steps nil
-                org-refile-allow-creating-parent-nodes 'confirm)
-
           ;; Add some todo keywords.
           (setq org-todo-keywords
                 '((sequence "TODO(t)"
@@ -1000,6 +991,21 @@ in
         '';
       };
 
+      org-refile = {
+        enable = true;
+        after = [ "org" ];
+        config = ''
+          ;; Refiling should include not only the current org buffer but
+          ;; also the standard org files. Further, set up the refiling to
+          ;; be convenient with IDO. Follows norang's setup quite closely.
+          (setq org-refile-targets '((nil :maxlevel . 2)
+                                     (org-agenda-files :maxlevel . 2))
+                org-refile-use-outline-path t
+                org-outline-path-complete-in-steps nil
+                org-refile-allow-creating-parent-nodes 'confirm)
+        '';
+      };
+
       org-superstar = {
         enable = true;
         hook = [ "(org-mode . org-superstar-mode)" ];