Disable system_tarball_pc and fix eval

It refers to a kernel version that no longer exists.

(cherry picked from commit e4b9624ca89617005cb082e2a8301695759e1b19)

nixos/release.nix

···
   # boot that system from uboot (like for the sheevaplug).
   # The pc variant helps preparing the expression for the system tarball
   # in a machine faster than the sheevpalug
+  /*
   system_tarball_pc = forAllSystems (system: makeSystemTarball {
     module = ./modules/installer/cd-dvd/system-tarball-pc.nix;
     inherit system;
   });
+  */
 
   # Provide container tarball for lxc, libvirt-lxc, docker-lxc, ...
   containerTarball = forAllSystems (system: makeSystemTarball {

pkgs/top-level/release-cross.nix

···
       #xorgserver.crossDrv = nativePlatforms;
     };
     nixUnstable.crossDrv = nativePlatforms;
-    linuxPackages_3_4.kernel.crossDrv = linux;
   };
 
   /* Basic list of packages to be natively built,