build(shells): Use dub, ldc, dmd from Nixpkgs

Author: PetarKirov

shells/default.nix

@@ -37,10 +37,11 @@
               nix-output-monitor
               repl
               rage
-              inputs'.dlang-nix.packages.dub
+              dub
+              ldc
             ]
             ++ pkgs.lib.optionals (pkgs.stdenv.system == "x86_64-linux") [
-              inputs'.dlang-nix.packages.dmd
+              dmd
             ];
 
           shellHook = ''