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/rounded-mgenplus/default.nix

@@ -1,33 +1,19 @@
-{ stdenv, fetchurl, p7zip }:
+{ lib, fetchzip, p7zip }:
 
 let
   pname = "rounded-mgenplus";
   version = "20150602";
-
-in
-
-stdenv.mkDerivation rec {
+in fetchzip rec {
   name = "${pname}-${version}";
-  inherit version;
 
-  src = fetchurl {
-    url = "https://osdn.jp/downloads/users/8/8598/${name}.7z";
-    sha256 = "1k15xvzd3s5ppp151wv31wrfq2ri8v96xh7i71i974rxjxj6gspc";
-  };
-
-  nativeBuildInputs = [ p7zip ];
-
-  phases = [ "unpackPhase" "installPhase" ];
-
-  unpackPhase = ''
-    7z x $src
-  '';
-
-  installPhase = ''
+  url = "https://osdn.jp/downloads/users/8/8598/${name}.7z";
+  postFetch = ''
+    ${p7zip}/bin/7z x $downloadedFile
     install -m 444 -D -t $out/share/fonts/${pname} ${pname}-*.ttf
   '';
+  sha256 = "0vwdknagdrl5dqwpb1x5lxkbfgvbx8dpg7cb6yamgz71831l05v1";
 
-  meta = with stdenv.lib; {
+  meta = with lib; {
     description = "A Japanese font based on Rounded M+ and Noto Sans Japanese";
     homepage = http://jikasei.me/font/rounded-mgenplus/;
     license = licenses.ofl;