remove grub and syslinux from NixOS

nix/no-bootloaders.nix

@@ -0,0 +1,13 @@
+{
+  # HACK: Drop this once, we have https://github.com/NixOS/nixpkgs/pull/312863 merged
+
+  # Both syslinux and grub also reference perl
+  nixpkgs.overlays = [
+    (final: prev: {
+      # we don't need grub: save ~ 60MB
+      grub2 = prev.coreutils;
+      grub2_efi = prev.coreutils;
+      syslinux = prev.coreutils;
+    })
+  ];
+}

nix/noninteractive.nix

@@ -11,6 +11,7 @@
 
   imports = [
     ./zfs-minimal.nix
+    ./no-bootloaders.nix
   ];
 
   # among others, this prevents carrying a stdenv with gcc in the image