Fix hardcoded unused struct members

`safe_struct_generator.py` uses a hardcoded list of unused struct members so it can determine if a pointer is safe to follow

https://github.com/KhronosGroup/Vulkan-Utility-Libraries/blob/70a16b03c513c477e74652da46f5d8f2b0e398fa/scripts/generators/safe_struct_generator.py#L87-L91

It would be better if vulkan_object exposed the `deprecated` xml attribute so we don't have to keep this list up to date
```xml
uint32_t enabledLayerCount
const char* const* ppEnabledLayerNamesOrdered list of layer names to be enabled
```