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/modules/system/boot/kernel.nix

@@ -20,7 +20,6 @@ in
   options = {
 
     boot.kernelPackages = mkOption {
-      type = types.packageSet;
       default = pkgs.linuxPackages;
       # We don't want to evaluate all of linuxPackages for the manual
       # - some of it might not even evaluate correctly.

nixos/modules/system/boot/systemd-unit-options.nix

@@ -17,15 +17,14 @@ in rec {
 
   unitOption = mkOptionType {
     name = "systemd option";
-    typerep = "(systemdOption)";
-    merge = _module: loc: defs:
+    merge = loc: defs:
       let
         defs' = filterOverrides defs;
         defs'' = getValues defs';
       in
         if isList (head defs'')
         then concatLists defs''
-        else mergeOneOption _module loc defs';
+        else mergeOneOption loc defs';
   };
 
   sharedOptions = {