* clean up backward and rm unncessary cat by directly outputting unsplitted policy_vb from _off_policy_rollout
* clean up backward and rm unncessary cat by directly outputting unsplitted policy_vb from _off_policy_rollout

jingweiz/pytorch-rl,AlekseyZhelo/pytorch-rl,AlekseyZhelo/pytorch-rl,lukashermann/pytorch-rl,lukashermann/pytorch-rl,jingweiz/pytorch-rl