header: Remove ValidationFlags changes from vulkan.h
header: Remove ValidationFlags changes from vulkan.h

The validation_flags features will be moved into an extension.

Change-Id: I435e75da8d8917f876e5bc904922cda26a87845a

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