flake.nix: try moving import of sd-image-aarch64.nix to the nixosModule

flake.nix

@@ -214,7 +214,6 @@
 
         pulsebert = nixosSystem' {
           modules = [
-            "${inputs.nixpkgs}/nixos/modules/installer/sd-card/sd-image-aarch64.nix"
             ./hosts/pulsebert
           ];
           system = "aarch64-linux";
@@ -222,7 +221,6 @@
 
         radiobert = nixosSystem' {
           modules = [
-            "${inputs.nixpkgs}/nixos/modules/installer/sd-card/sd-image-aarch64.nix"
             ./hosts/radiobert
           ];
           system = "aarch64-linux";

lib/default.nix

@@ -2,7 +2,7 @@
 # That includes physical servers, VMs, containers, and personal machines.
 #
 
-{ config, lib, pkgs, ... }:
+{ inputs, config, lib, pkgs, ... }:
 
 let
   hqPrefix64 = "fd23:42:c3d2:523";
@@ -31,7 +31,8 @@ in {
     ./users
     ./stats.nix
     ./openwebrx.nix
-  ];
+  ]
+  ++ lib.optional config.boot.loader.raspberryPi.enable "${inputs.nixpkgs}/nixos/modules/installer/sd-card/sd-image-aarch64.nix";
 
   options.c3d2 = with lib;
     with lib.types; {