This reverts commit 9f4b1064c6.
It caused problems: https://github.com/NixOS/nixpkgs/pull/318872#issuecomment-2196168990
FODs are not allowed to have references, but writeText is often used to create a file with references.
Leading to this error:
error: fixed output derivation 'packages.json' is not allowed to refer to other store paths.
f814e5cb8f