Remove one method of specifying features in vktSpvAsm

Remove one method of specifying features in vktSpvAsm

The features can either be specified as a vector of strings (most of
which won't work), or as a VulkanFeatures struct, which is properly
checked. Remove the vector of strings method and change everything to
use the VulkanFeatures.

Components: Vulkan
Affects: dEQP-VK.spirv_assembly.*

Change-Id: Ia4f51f9e64dde129cb577982f2a17fa529c4c961
(cherry picked from commit f58817ce095d2a0dda0b5d2a57f82428b3462f38)