data/fonts: cleanup

* 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

pkgs/data/fonts/eb-garamond/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchzip }:
+{ lib, fetchzip }:
 
 let
   version = "0.016";
@@ -15,7 +15,7 @@ in fetchzip rec {
 
   sha256 = "04jq4mpln85zzbla8ybsjw7vn9qr3r0snmk5zykrm24imq7ripv3";
 
-  meta = with stdenv.lib; {
+  meta = with lib; {
     homepage = http://www.georgduffner.at/ebgaramond/;
     description = "Digitization of the Garamond shown on the Egenolff-Berner specimen";
     maintainers = with maintainers; [ relrod rycee ];