elites in iCEM optimizer are never reset

[nuria95]

Steps to reproduce

When iCEM optimizer is initialised , self.elites is initialised to None.
But after finishing the iCEM optimisation, the attribute is never reset back to None.
Even more, this variable is never reset again (even after resetting the TrajectoryOptimizerAgent.

Expected Results

I would expect the self.elites parameter to be reset to None before the return in iCEM optimize method.