nixos: remove StandardOutput=syslog, StandardError=syslog lines

Since systemd 243, docs were already steering users towards using
`journal`:

eedaf7f322

systemd 246 will go one step further, it shows warnings for these units
during bootup, and will [automatically convert these occurences to
`journal`](f3dc6af20f):

> [    6.955976] systemd[1]: /nix/store/hwyfgbwg804vmr92fxc1vkmqfq2k9s17-unit-display-manager.service/display-manager.service:27: Standard output type syslog is obsolete, automatically updating to journal. Please update│······················
 your unit file, and consider removing the setting altogether.

So there's no point of keeping `syslog` here, and it's probably a better
idea to just not set it, due to:

> This setting defaults to the value set with DefaultStandardOutput= in
> systemd-system.conf(5), which defaults to journal.

nixos/modules/hardware/ckb-next.nix

@@ -43,7 +43,6 @@ in
         serviceConfig = {
           ExecStart = "${cfg.package}/bin/ckb-next-daemon ${optionalString (cfg.gid != null) "--gid=${builtins.toString cfg.gid}"}";
           Restart = "on-failure";
-          StandardOutput = "syslog";
         };
       };
     };

nixos/modules/security/tpm2.nix

@@ -170,7 +170,6 @@ in {
           Restart = "always";
           RestartSec = 30;
           BusName = "com.intel.tss2.Tabrmd";
-          StandardOutput = "syslog";
           ExecStart = "${cfg.abrmd.package}/bin/tpm2-abrmd";
           User = "tss";
           Group = "nogroup";

nixos/modules/services/security/privacyidea.nix

@@ -234,7 +234,6 @@ in
           ExecStop = "${pkgs.coreutils}/bin/kill -INT $MAINPID";
           NotifyAccess = "main";
           KillSignal = "SIGQUIT";
-          StandardError = "syslog";
         };
       };
 

nixos/modules/services/system/earlyoom.nix

@@ -106,7 +106,6 @@ in
       path = optional ecfg.enableNotifications pkgs.dbus;
       serviceConfig = {
         StandardOutput = "null";
-        StandardError = "syslog";
         ExecStart = ''
           ${pkgs.earlyoom}/bin/earlyoom \
           -m ${toString ecfg.freeMemThreshold} \

nixos/modules/services/wayland/cage.nix

@@ -73,8 +73,6 @@ in {
         TTYVTDisallocate = "yes";
         # Fail to start if not controlling the virtual terminal.
         StandardInput = "tty-fail";
-        StandardOutput = "syslog";
-        StandardError = "syslog";
         # Set up a full (custom) user session for the user, required by Cage.
         PAMName = "cage";
       };

nixos/modules/services/web-apps/tt-rss.nix

@@ -632,8 +632,6 @@ let
           User = "${cfg.user}";
           Group = "tt_rss";
           ExecStart = "${pkgs.php}/bin/php ${cfg.root}/update.php --daemon --quiet";
-          StandardOutput = "syslog";
-          StandardError = "syslog";
           Restart = "on-failure";
           RestartSec = "60";
           SyslogIdentifier = "tt-rss";

nixos/modules/services/x11/display-managers/gdm.nix

@@ -200,7 +200,6 @@ in
       KillMode = "mixed";
       IgnoreSIGPIPE = "no";
       BusName = "org.gnome.DisplayManager";
-      StandardOutput = "syslog";
       StandardError = "inherit";
       ExecReload = "${pkgs.coreutils}/bin/kill -SIGHUP $MAINPID";
       KeyringMode = "shared";

nixos/modules/services/x11/display-managers/lightdm.nix

@@ -253,7 +253,6 @@ in
       KeyringMode = "shared";
       KillMode = "mixed";
       StandardError = "inherit";
-      StandardOutput = "syslog";
     };
 
     environment.etc."lightdm/lightdm.conf".source = lightdmConf;

nixos/tests/virtualbox.nix

@@ -198,7 +198,6 @@ let
       systemd.services."vboxtestlog-${name}@" = {
         description = "VirtualBox Test Machine Log For ${name}";
         serviceConfig.StandardInput = "socket";
-        serviceConfig.StandardOutput = "syslog";
         serviceConfig.SyslogIdentifier = "GUEST-${name}";
         serviceConfig.ExecStart = "${pkgs.coreutils}/bin/cat";
       };