conditioning example should do something

[josephdviviano]

Right now, the conditioning example in train_conditioning.py is a red herring - the conditioning does nothing.

As suggested in a code review, we should make one of the conditions remove (at least one) of the modes in the hypergrid environment, so we can verify at test time that the conditioning is actually being used: #188 (comment)

This will require the conditioning to interact with the environment somehow which expands the scope of this a bit but should be interesting (and a high priority follow up to the original conditioning PR).