make-squashfs: drop references to build closure

Changed files
+4
nixos
+4
nixos/lib/make-squashfs.nix
···
name = "${fileName}${lib.optionalString (!hydraBuildProduct) ".img"}";
__structuredAttrs = true;
+
# the image will be self-contained so we can drop references
+
# to the closure that was used to build it
+
unsafeDiscardReferences.out = true;
+
nativeBuildInputs = [ squashfsTools ];
buildCommand =