anv: Drop unneeded struct keywords

anv: Drop unneeded struct keywords

All VkFoo structs are typedef'd to not need the struct keyword.  Leaving
it in there is just extra characters and breaks Vulkan's aliasing when
stuff gets promoted to core versions.  It's better to just never use
struct for VkFoo.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>