layers: Change struct_size_helper to use new codegen
layers: Change struct_size_helper to use new codegen

Remove old references, add calls to new generator.

Change-Id: I64ab859e4ae6893870697f16ee6fd596b8a7908b

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools