rkt: libsystemd fix (#19658)

As of systemd 231, the LD_LIBRARY_PATH fix applied in the installPhase of rkt's
build was no longer valid, causing rkt to fail to work. This patch changes the
path to point to the new location of libsystemd, which is in ${systemd.lib}.

pkgs/applications/virtualization/rkt/default.nix

@@ -58,7 +58,7 @@ in stdenv.mkDerivation rec {
     cp -Rv $BUILDDIR/target/bin/stage1-*.aci $out/${stage1Dir}/
 
     wrapProgram $out/bin/rkt \
-      --prefix LD_LIBRARY_PATH : ${systemd}/lib \
+      --prefix LD_LIBRARY_PATH : ${systemd.lib}/lib \
       --prefix PATH : ${iptables}/bin
   '';