Replace ad hoc throttling fix with throttled

`throttled` is a service designed to fix the same CPU throttling bug,
but it's an actively maintainted upstream project that we can use.

lenovo/thinkpad/t480s/default.nix

@@ -4,7 +4,8 @@
   imports = [
     ../../../common/cpu/intel
     ../../../common/pc/laptop/acpi_call.nix
-    ../../../common/pc/laptop/cpu-throttling-bug.nix
     ../.
   ];
+
+  services.throttled.enable = lib.mkDefault true;
 }