Since the Pango issue 457[1] has been fixed and Nixpkgs patched, it's no
longer necessary to keep X11 and .otb fonts in separate outputs (previously
they would cause application to display broken fonts).
[1]: https://gitlab.gnome.org/GNOME/pango/-/issues/457
* 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
