Remove astring from nix

Signed-off-by: Marcello Seri <marcello.seri@gmail.com>

Author: mseri

nix/default.nix

@@ -23,7 +23,6 @@ buildDunePackage ({
 
   propagatedBuildInputs = [
     bibfmt
-    astring
     cohttp-lwt-unix
     cmdliner
     clz