Removed the PyObjC dependency.

This addresses problems with building a one dir build for macOS.
It became problematic because depending on the macOS version, it pulls different dependencies, and we would either have to build a macos onedir for each macOS supported release, or ship a crippled onedir(because it would be tied to the macOS version where the onedir was built).
Since it's currently not being used, it's removed.
