nixos/users-groups: drop the weak-hash activation warning

The libxcrypt transition was in 23.05, so I think we've given
people sufficient time to fix hashes of mutable users.

Part of #475305.

nixos/modules/config/users-groups.nix

@@ -950,32 +950,8 @@ in
         };
       };
 
-      # Warn about user accounts with deprecated password hashing schemes
-      # This does not work when the users and groups are created by
-      # systemd-sysusers because the users are created too late then.
-      system.activationScripts.hashes =
-        if !config.systemd.sysusers.enable && !config.services.userborn.enable then
-          {
-            deps = [ "users" ];
-            text = ''
-              users=()
-              while IFS=: read -r user hash _; do
-                if [[ "$hash" = "$"* && ! "$hash" =~ ^\''$${cryptSchemeIdPatternGroup}\$ ]]; then
-                  users+=("$user")
-                fi
-              done </etc/shadow
-
-              if (( "''${#users[@]}" )); then
-                echo "
-              WARNING: The following user accounts rely on password hashing algorithms
-              that have been removed. They need to be renewed as soon as possible, as
-              they do prevent their users from logging in."
-                printf ' - %s\n' "''${users[@]}"
-              fi
-            '';
-          }
-        else
-          ""; # keep around for backwards compatibility
+      # for backwards compatibility
+      system.activationScripts.hashes = stringAfter [ "users" ] "";
 
       # for backwards compatibility
       system.activationScripts.groups = stringAfter [ "users" ] "";