chore: remove shellHook from flake.nix

Removed the shellHook that automatically exec'd zsh, allowing users to
use their preferred shell.

Author: ianks

flake.nix

@@ -27,10 +27,7 @@
             nodejs
           ];
 
-          # Make is so nix develop --impure uses zsh config
-          shellHook = ''
-            exec zsh
-          '';
+
         };
       }
     );