header: Move vk.xml to verison 1.0.26
header: Move vk.xml to verison 1.0.26

Change-Id: Ie2bc2b5c15c4bad19083081727c88647113e3725

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