rtorrent: make updateScript update both this package and libtorrent-rakshasa

It is common for newer versions of rtorrent to depend in newer versions
of libtorrent-rakshasa to be built. So updating them separately
sometimes works, sometimes it doesn't and need some intervention until
someone goes and updates both.

Using _experimental-update-script-combinators to update both packages at
the same time should avoid this issue in future.

pkgs/by-name/li/libtorrent-rakshasa/package.nix

@@ -6,7 +6,6 @@
   curl,
   fetchFromGitHub,
   lib,
-  nix-update-script,
   openssl,
   pkg-config,
   stdenv,
@@ -38,8 +37,6 @@ stdenv.mkDerivation (finalAttrs: {
 
   configureFlags = [ "--enable-aligned=yes" ];
 
-  passthru.updateScript = nix-update-script { };
-
   enableParallelBuilding = true;
 
   meta = {

pkgs/by-name/rt/rtorrent/package.nix

@@ -1,4 +1,5 @@
 {
+  _experimental-update-script-combinators,
   autoreconfHook,
   cppunit,
   curl,
@@ -9,8 +10,8 @@
   libtorrent-rakshasa,
   lua5_4_compat,
   ncurses,
-  nixosTests,
   nix-update-script,
+  nixosTests,
   openssl,
   pkg-config,
   stdenv,
@@ -72,7 +73,10 @@ stdenv.mkDerivation (finalAttrs: {
   passthru = {
     inherit libtorrent-rakshasa;
     tests = { inherit (nixosTests) rtorrent; };
-    updateScript = nix-update-script { };
+    updateScript = _experimental-update-script-combinators.sequence [
+      (nix-update-script { attrPath = "libtorrent-rakshasa"; })
+      (nix-update-script { })
+    ];
   };
 
   meta = {