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/ttf-bitstream-vera/default.nix

@@ -1,4 +1,4 @@
-{stdenv, fetchzip}:
+{ lib, fetchzip }:
 
 fetchzip {
   name = "ttf-bitstream-vera-1.10";
@@ -7,14 +7,11 @@ fetchzip {
 
   postFetch = ''
     tar -xjf $downloadedFile --strip-components=1
-    fontDir=$out/share/fonts/truetype
-    mkdir -p $fontDir
-    cp *.ttf $fontDir
+    install -m444 -Dt $out/share/fonts/truetype *.ttf
   '';
 
   sha256 = "179hal4yi3367jg8rsvqx6h2w4s0kn9zzrv8c47sslyg28g39s4m";
 
   meta = {
-    platforms = stdenv.lib.platforms.unix;
   };
 }