plasma5Packages.kactivities-stats: restrict platforms

pkgs/development/libraries/kde-frameworks/kactivities-stats.nix

···
 {
-  mkDerivation,
+  mkDerivation, lib,
   extra-cmake-modules,
   boost, kactivities, kconfig, qtbase,
 }:
···
   buildInputs = [ boost kactivities kconfig ];
   propagatedBuildInputs = [ qtbase ];
   outputs = [ "out" "dev" ];
+  meta.platforms = lib.platforms.linux ++ lib.platforms.freebsd;
 }