carlito used to call `fetchzip` directly, and the fact that it was a
fixed-output derivation meant nobody noticed that:
1. the derivation no longer built from source (due to changes in
`fetchzip`), and
2. the updated fontconfig xml never got used.
* make font derivations fixed-output where applicable
* fix dead links
* `stdenv.lib` -> `lib` where `stdenv` is not involved
* remove `meta.platforms = [ unix ]` and `meta.platforms = [ linux ]` because the restriction has no sense for data packages
