Cycles: Remove redundant float4->float3 conversion
Cycles: Remove redundant float4->float3 conversion

Not as if it gives noticeable changes render-time, but it's just weird to
convert float4 to float 3 to just access individual x/y/z components.

Plus some compilers might be more stupid than GCC and don't optimize this
out well.

pyrochlore/cycles,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,pyrochlore/cycles,tangent-opensource/coreBlackbird,pyrochlore/cycles