fix: remove custom app definition

This seems to do something similar to the default behaviour of `nix run`
where it just runs a package.

nix/modules/scenarios.nix

@@ -15,6 +15,4 @@ let
 in
 {
   packages = builtins.listToAttrs scenarios;
-
-  apps = builtins.listToAttrs (builtins.map ({ name, value }: { inherit name; value = { program = value; }; }) scenarios);
 }