build: Remove reference to non-existent file.

* daemon.am (EXTRA_DIST): Remove nix/sync-with-upstream.

daemon.am

 # GNU Guix --- Functional package management for GNU
-# Copyright © 2012, 2013, 2014 Ludovic Courtès <ludo@gnu.org>
+# Copyright © 2012, 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
 #
 # This file is part of GNU Guix.
 #
@@ -180,7 +180,6 @@ nodist_libexec_SCRIPTS =			\
   nix/scripts/guix-authenticate
 
 EXTRA_DIST +=					\
-  nix/sync-with-upstream			\
   nix/libstore/schema.sql			\
   nix/AUTHORS					\
   nix/COPYING