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/marathi-cursive/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchzip, p7zip }:
+{ lib, fetchzip, p7zip }:
 
 let
   version = "1.2";
@@ -11,15 +11,13 @@ in fetchzip rec {
     ${p7zip}/bin/7z x $downloadedFile
     cd MarathiCursive
 
-    mkdir -p $out/share/fonts/marathi-cursive
-    cp -v *.otf *.ttf $out/share/fonts/marathi-cursive
-    mkdir -p $out/share/doc/${name}
-    cp -v README *.txt $out/share/doc/${name}
+    install -m444 -Dt $out/share/fonts/marathi-cursive *.otf *.ttf
+    install -m444 -Dt $out/share/doc/${name}           README *.txt
   '';
 
-  sha256 = "0fhz2ixrkm523qlx5pnwyzxgb1cfiiwrhls98xg8a5l3sypn1g8v";
+  sha256 = "0wq4w79x8r5w6ikm9amcmapf0jcdgifs9zf1pbnw3fk4ncz5s551";
 
-  meta = with stdenv.lib; {
+  meta = with lib; {
     homepage = https://github.com/MihailJP/MarathiCursive;
     description = "Modi script font with Graphite and OpenType support";
     maintainers = with maintainers; [ mathnerd314 ];