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/iwona/default.nix

@@ -1,23 +1,18 @@
-{ stdenv, fetchzip }:
+{ lib, fetchzip }:
 
-stdenv.mkDerivation rec {
-  name = "iwona-${version}";
+let
   version = "0_995";
+in fetchzip {
+  name = "iwona-${version}";
+  url = "http://jmn.pl/pliki/Iwona-otf-${version}.zip";
 
-  src = fetchzip {
-    url = "http://jmn.pl/pliki/Iwona-otf-${version}.zip";
-    sha256 = "1wj5bxbxpz5a8p3rhw708cyjc0lgqji8g0iv6brmmbrrkpb3jq2s";
-  };
-
-  installPhase = ''
-    install -m 444 -D -t $out/share/fonts/opentype/ *.otf
+  postFetch = ''
+    mkdir -p $out/share/fonts/opentype
+    unzip -j $downloadedFile *.otf -d $out/share/fonts/opentype
   '';
+  sha256 = "1dcpn13bd31dw7ir0s722bv3nk136dy6qsab0kznjbzfqd7agswa";
 
-  outputHashAlgo = "sha256";
-  outputHashMode = "recursive";
-  outputHash = "1dcpn13bd31dw7ir0s722bv3nk136dy6qsab0kznjbzfqd7agswa";
-
-  meta = with stdenv.lib; {
+  meta = with lib; {
     description = "A two-element sans-serif typeface, created by Małgorzata Budyta";
     homepage = http://jmn.pl/en/kurier-i-iwona/;
     # "[...] GUST Font License (GFL), which is a free license, legally