Revert "Add the tool "nixos-typecheck" that can check an option declaration to:"

This reverts commit cad8957eab. It
breaks NixOps, but more importantly, such major changes to the module
system really need to be reviewed.

nixos/default.nix

@@ -34,8 +34,6 @@ in
 
   system = eval.config.system.build.toplevel;
 
-  typechecker = eval.config.system.build.typechecker;
-
   vm = vmConfig.system.build.vm;
 
   vmWithBootLoader = vmWithBootLoaderConfig.system.build.vm;