Rename Light HAL default implementation variable.

The Light HAL implements a function getLights that returns a vector
of HwLight objects. This vector is called "lights" in Lights.cpp,
but it is called "types" in Lights.h. Lights.h has been changed to
call the vector "lights".

Test: VtsHalLightTargetTest
Change-Id: I1e567d1454d42e3efc0186cde8340c32e7f3456e