move wsl binfmt configuration to host

apparently a mkIf can't contain a nonexistent option even if it's never
gonna be evaluated?

hosts/nixos-wsl/configuration.nix

@@ -7,6 +7,7 @@
       profile.base.enable = true;
       binfmt.enable = true;
     };
+    wsl.interop.register = true;
 
     networking.networkmanager.enable = false;
     programs.gnupg.agent = {

system/hardware/binfmt.nix

@@ -33,10 +33,5 @@ in
     (lib.mkIf enable {
       boot.binfmt = {inherit emulatedSystems;};
     })
-
-    # keep Windows binfmt registration on wsl
-    (lib.mkIf (cfg.enable && lib.hasAttrByPath [ "wsl" "interop" "register" ] options) {
-      wsl.interop.register = lib.mkDefault true;
-    })
   ];
 }