OpenSCToken (https://github.com/frankmorgner/OpenSCToken) is now a
standalone package that provides the CryptoTokenKit app extension.
It includes its own 'build-package' script, which handles building
the OpenSC library and statically linking against it.
The 'MacOSX/' directory in OpenSC itself is only used to build the
macOS tokend. Remove unused code for building a CryptoTokenKit app
extension from this directory (which no longer works). This should
help to avoid confusion when building OpenSC for macOS.