moltenvk: ship correctly for macos universal

libvulkan.dylib and libvulkan.1.dylib don't seem to respond well to XCode 12.0 build tools modifying the binary as our current build set up requires. Luckily we don't actually need them so disable that for now.

We also need to remove the @rpath entry in libMoltenVK.dylib's id to avoid dependant libraries from using that name as their link name and then causing our relocation/merge to create a libgstvulkan/applemedia that links against a non-existent @rpath/libMoltenVK.dylib.