Remove spvDescriptor wrapper in spvDescriptorArray

[js6i]

That's a workaround for #2308. The diff between shader byte code with and without this change is only the getelementptr indexing order for affected variables, and looks something like this: (old above, new below)

<   %8 = getelementptr inbounds %struct.spvDescriptorSetBuffer1, ptr addrspace(1) %0, i64 0, i32 0, i64 %7, i32 0, i32 0
---
>   %8 = getelementptr inbounds %struct.spvDescriptorSetBuffer1, ptr addrspace(1) %0, i64 %7, i32 0, i64 0, i32 0, i32 0