Old driver functionality

[benson31]

The drivers that were unused were:
https://github.com/LLNL/lbann/blob/d688228cf630391856a611aba7bd55cf2dfd9bad/model_zoo/lbann_aecycgan.cpp
https://github.com/LLNL/lbann/blob/d688228cf630391856a611aba7bd55cf2dfd9bad/model_zoo/lbann_cycgan.cpp
https://github.com/LLNL/lbann/blob/d688228cf630391856a611aba7bd55cf2dfd9bad/model_zoo/lbann_gan.cpp
https://github.com/LLNL/lbann/blob/d688228cf630391856a611aba7bd55cf2dfd9bad/model_zoo/lbann_inf.cpp

It is believed that the features implemented have either been completely abandoned or entirely supported in the main lbann driver.