Remove warning in Stacked Ensemble predict function about missing fold_column frame
There's a warning message when you use predict() in Stacked Ensemble when the base models were trained with a fold_column. I checked in R, but it's probably also happening in Python. Only Stacked Ensemble is affected (other models are not).
Note to myself: This gets emitted from hex.Model#adaptTestForTrain because stacked ensemble uses metalearner_fold_column instead of fold_column. So it affects both R and Python. Simple fix would be to set internally fold_column to the value of metalearner_fold_column but it is not a clean solution.