nixos/update-users-groups: fix cross compilation

Since #246772, cross compiled NixOS is broken because the DateTime perl
package that was used in the update-users-groups.pl script depends on
Testutf8 which does not cross compile (see #198548).

This PR drops the DateTime dependency in favour of TimePiece, which has
less dependencies and whose closure does cross compile.

nixos/modules/config/update-users-groups.pl

@@ -4,7 +4,7 @@
 use File::Slurp;
 use Getopt::Long;
 use JSON;
-use DateTime;
+use Time::Piece;
 
 # Keep track of deleted uids and gids.
 my $uidMapFile = "/var/lib/nixos/uid-map";
@@ -26,17 +26,8 @@ sub updateFile {
 # Converts an ISO date to number of days since 1970-01-01
 sub dateToDays {
     my ($date) = @_;
-    my ($year, $month, $day) = split('-', $date, -3);
-    my $dt = DateTime->new(
-        year      => $year,
-        month     => $month,
-        day       => $day,
-        hour      => 0,
-        minute    => 0,
-        second    => 0,
-        time_zone => 'UTC',
-    );
-    return $dt->epoch / 86400;
+    my $time = Time::Piece->strptime($date, "%Y-%m-%d");
+    return $time->epoch / 60 / 60 / 24;
 }
 
 sub nscdInvalidate {

nixos/modules/config/users-groups.nix

@@ -648,7 +648,7 @@ in {
         install -m 0700 -d /root
         install -m 0755 -d /home
 
-        ${pkgs.perl.withPackages (p: [ p.FileSlurp p.JSON p.DateTime ])}/bin/perl \
+        ${pkgs.perl.withPackages (p: [ p.FileSlurp p.JSON p.TimePiece ])}/bin/perl \
         -w ${./update-users-groups.pl} ${spec}
       '';
     };