systemd: Use upstream tmpfiles.d rules

This fixes a failing assert in systemd-timesyncd (issue #5913) as it
expects the directory /run/systemd/netif/links/ to exist, and nothing in
NixOS currently creates it.

Also we get a net reduction in our code as rules for /run/utmp and
/var/log/journal are also provided by the same upstream file.

(cherry picked from commit a278a9224a3c1c5db399d53c86b36a25133b5cda)

nixos/modules/system/activation/activation-script.nix

···
       ''
         # Various log/runtime directories.
 
-        touch /run/utmp # must exist
-        chgrp ${toString config.ids.gids.utmp} /run/utmp
-        chmod 664 /run/utmp
-
         mkdir -m 0755 -p /run/nix/current-load # for distributed builds
         mkdir -m 0700 -p /run/nix/remote-stores
 

nixos/modules/system/boot/systemd.nix

···
     system.activationScripts.systemd = stringAfter [ "groups" ]
       ''
         mkdir -m 0755 -p /var/lib/udev
-        mkdir -p /var/log/journal
-        chmod 0755 /var/log/journal
-
-        # Make all journals readable to users in the wheel and adm
-        # groups, in addition to those in the systemd-journal group.
-        # Users can always read their own journals.
-        ${pkgs.acl}/bin/setfacl -nm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal || true
 
         if ! [ -e /etc/machine-id ]; then
           ${systemd}/bin/systemd-machine-id-setup
···
         startSession = true;
       };
 
+    environment.etc."tmpfiles.d/systemd.conf".source = "${systemd}/example/tmpfiles.d/systemd.conf";
     environment.etc."tmpfiles.d/x11.conf".source = "${systemd}/example/tmpfiles.d/x11.conf";
 
     environment.etc."tmpfiles.d/nixos.conf".text =
       ''
         # This file is created automatically and should not be modified.
         # Please change the option ‘systemd.tmpfiles.rules’ instead.
-
-        z /var/log/journal 2755 root systemd-journal - -
-        z /var/log/journal/%m 2755 root systemd-journal - -
-        z /var/log/journal/%m/* 0640 root systemd-journal - -
 
         ${concatStringsSep "\n" cfg.tmpfiles.rules}
       '';