package/macosx: fix bogus plugins.dat generation

The MacOS/plugins folder doesn't exist, it's Frameworks/plugins.

The plugins.dat is created with the VLC.app build target. And it takes care of native vs build targets. Altough an Apple Silicon machine should be capable of generating for x86_64, but not the other way around. Still needed after stripping as the plugins.dat use the file date to validate an entry.

And remove local/native contrib build folder from PATH. Let contrib and configure scripts handle it.