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/arkpandora/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl }:
+{ lib, fetchurl }:
 
 let
   version = "2.04";
@@ -21,6 +21,5 @@ in fetchurl {
 
   meta = {
     description = "Font, metrically identical to Arial and Times New Roman";
-    platforms = stdenv.lib.platforms.unix;
   };
 }