nixos/systemd: move default sysctls from coredump module

The default systemd sysctl snippet contains various security‐relevant
settings, it is however only installed if systemd.coredump.enable is
enabled, despite these settings not being strictly related to
systemd-coredump.

nixos/modules/system/boot/systemd.nix

@@ -667,6 +667,8 @@ in
 
         "systemd/system-environment-generators/env-generator".source =
           "${config.system.nixos-init.package}/bin/env-generator";
+
+        "sysctl.d/50-default.conf".source = "${cfg.package}/example/sysctl.d/50-default.conf";
       };
 
     services.dbus.enable = true;

nixos/modules/system/boot/systemd/coredump.nix

@@ -67,8 +67,6 @@ in
               }}"
             ];
           };
-
-        "sysctl.d/50-default.conf".source = "${systemd}/example/sysctl.d/50-default.conf";
       };
 
       users.users.systemd-coredump = {