move bootpart-systemd-boot installation into modules/image, so it reliably applies to hosts which need it

hosts/modules/hal/rpi-400.nix

@@ -11,7 +11,6 @@ in
       # rpi bootrom -> edk2 -> systemd-boot
       # edk2 exists here to provide the base UEFI environment which systemd-boot expects
       pkgs.bootpart-edk2-rpi
-      pkgs.bootpart-systemd-boot
     ];
     #v used by systemd-boot
     hardware.deviceTree.name = "broadcom/bcm2711-rpi-400.dtb";

hosts/modules/hal/x86_64.nix

@@ -37,7 +37,5 @@ in
       options kvm_amd nested=1
       options kvm_intel nested=1
     '';
-
-    sane.image.extraBootFiles = [ pkgs.bootpart-systemd-boot ];
   };
 }

modules/image.nix

@@ -395,7 +395,8 @@ in
         '')
       ]
       ++
-      lib.optionals config.boot.loader.systemd-boot.enable [
+      lib.optionals config.boot.loader.systemd-boot.enable ([
+        pkgs.bootpart-systemd-boot
         # it'd be cool to use `config.system.build.installBootLoader` to install both the bootloader config AND the bootloader itself,
         # but the combination of custom nixpkgs logic + systemd's sanity checking makes it near impossible to use
         # outside a live system.
@@ -443,7 +444,7 @@ in
             console-mode keep
           EOF
         '')
-      ]
+      ])
     ;
   };
 }