xen: deduplicate pkgs.xen and pkgs.xenPackages.xen

There is no point in having both. The top-level package now points
directly to the latest version.

Signed-off-by: Fernando Rodrigues <alpha@sigmasquadron.net>

pkgs/applications/virtualization/xen/README.md

@@ -88,7 +88,8 @@ open a PR fixing the script, and update Xen manually:
 
 ### For Both Update Methods
 
-1. Update `packages.nix` with the new versions. Don't forget the `slim` packages!
+1. Update `packages.nix` and `../../../top-level/all-packages.nix` with the new
+   versions. Don't forget the `slim` packages!
 1. Make sure all branches build. (Both the `standard` and `slim` versions)
 1. Use the NixOS module to test if dom0 boots successfully on all new versions.
 1. Make sure the `meta` attributes evaluate to something that makes sense. The

pkgs/applications/virtualization/xen/packages.nix

@@ -62,7 +62,4 @@ rec {
     withInternalIPXE = false;
     inherit (slim) meta;
   };
-
-  xen = xen_4_19;
-  xen-slim = xen_4_19-slim;
 }

pkgs/top-level/all-packages.nix

@@ -34771,8 +34771,8 @@ with pkgs;
 
   xenPackages = recurseIntoAttrs (callPackage ../applications/virtualization/xen/packages.nix {});
 
-  xen = xenPackages.xen;
-  xen-slim = xenPackages.xen-slim;
+  xen = xenPackages.xen_4_19;
+  xen-slim = xenPackages.xen_4_19-slim;
 
   xkbset = callPackage ../tools/X11/xkbset { };