IOSurface: remove xpc dependency

pkgs/os-specific/darwin/apple-sdk-11.0/frameworks.nix

···
   IOBluetooth                      = { inherit CoreBluetooth IOKit; };
   IOBluetoothUI                    = { inherit IOBluetooth; };
   IOKit                            = {};
-  # `IOSurface` should depend on `Libsystem` (in place of `xpc`) but this currently causes build
-  # issues due to incompatibility issues between `Libsystem` and `libcxx`.
-  IOSurface                        = { inherit IOKit xpc; };
+  IOSurface                        = { inherit IOKit; };
   IOUSBHost                        = {};
   IdentityLookup                   = {};
   ImageCaptureCore                 = {};