Revert "google-cloud-cpp: schedule on big-parallel machines"

This reverts commit add8dd840205aa9539d37591829eff3b48dd1359.
This attribute doesn't belong into meta and has no effect there.

pkgs/development/libraries/google-cloud-cpp/default.nix

···
     homepage = "https://github.com/googleapis/google-cloud-cpp";
     description = "C++ Idiomatic Clients for Google Cloud Platform services";
     platforms = [ "x86_64-linux" "aarch64-linux" ];
-    requiredSystemFeatures = [ "big-parallel" ];
     maintainers = with maintainers; [ cpcloud ];
   };
 }