remove method GraphManager.emulate_act_on_trainer

[zach-nervana]

A comment from the code:

# TODO-remove - this is a temporary flow, used by the trainer worker, duplicated from observe() - need to create
#               an external trainer flow reusing the existing flow and methods [e.g. observe(), step(), act()]

It appears that this code is related to, if not the cause of, quite a bit of complexity and duplicate code in the training control flow and steps counting.