layers: Fix unique_objects_wrappers.h
layers: Fix unique_objects_wrappers.h

The unique_objects_wrappers.h header was generated with code that
caused several compilation warnings.  This resolves those warnings.

Change-Id: I5ed3bdb6bbe7df48b3fe6fb6679916161b32fdfd

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers