Remove explicit packages list in nix shell #223

Explicitly listing some local packages and not others means the latter
one won't have their dependencies managed by haskell.nix which
potentially leads to incompatibilities. Implicitly, all local packages
have their dependencies managed by nix which should make the build
more consistent.

shell.nix

@@ -46,13 +46,6 @@ let
   ];
 
   haskellNixShell = hsPkgs.shellFor {
-    packages = ps: with ps; [
-      hydra-prelude
-      hydra-node
-      hydra-plutus
-      hydra-cluster
-      merkle-patricia-tree
-    ];
 
     # Haskell.nix managed tools (via hackage)
     tools = {