window_macosx: disable window when drawable is used

The current vout_display implementations for macosx are completely handling the window lifecycle for now, so the window isn't bringing any value. In addition, the window module doesn't embed itself into the drawable, so what really happens is that the display module is using the drawable provided through libvlc whereas the window module opens a new separate unused window, whose events are propagated to the display anyway.

By disabling the module when a drawable is present, we ensure the previous behaviour is still active without breaking window provision for macos users without embedding.