bakoma_ttf: make the font derivations fixed-output (#28130)

- [x] dead link fixed
- [x] make the font derivations fixed-output (https://github.com/NixOS/nixpkgs/issues/27754)

pkgs/data/fonts/bakoma-ttf/default.nix

@@ -1,20 +1,18 @@
-{stdenv, fetchurl}:
+{stdenv, fetchzip}:
 
-stdenv.mkDerivation {
+fetchzip {
   name = "bakoma-ttf";
 
-  src = fetchurl {
-    url = http://tarballs.nixos.org/bakoma-ttf.tar.bz2;
-    sha256 = "1j1y3cq6ys30m734axc0brdm2q9n2as4h32jws15r7w5fwr991km";
-  };
+  url = http://tarballs.nixos.org/sha256/1j1y3cq6ys30m734axc0brdm2q9n2as4h32jws15r7w5fwr991km;
 
-  dontBuild = true;
-
-  installPhase = ''
+  postFetch = ''
+    tar xjvf $downloadedFile --strip-components=1
     mkdir -p $out/share/fonts/truetype
     cp ttf/*.ttf $out/share/fonts/truetype
   '';
 
+  sha256 = "0g7i723n00cqx2va05z1h6v3a2ar69gqw4hy6pjj7m0ml906rngc";
+
   meta = {
     description = "TrueType versions of the Computer Modern and AMS TeX Fonts";
     homepage = http://www.ctan.org/tex-archive/fonts/cm/ps-type1/bakoma/ttf/;