Fix createLut in ColorSpace.

Previously createLut returns unique_ptr<float3>, which calls delete when it's
destroyed. However, the actual allocation happens using new float3[size * size
* size], which should cal delete [] when it's destroyed. This patch changes the
type to float3[] such that delete [] is called when it's destroyed.

BUG: 112717608
Test: N/A
Change-Id: Ida0671e33c0659c31d599eacc12fffbe35923876