Remove logging on train/eval/predict data arg

[terrytangyuan]

Right now we are seeing logs like

2019-09-24 17:25:34,392] [DEBUG] [main.py:88:main] Starting task queue with training data directory sqlflow_test_iris_train, evaluation data directory , and prediction data directory

which should not contain the word "directory" in case they are ODPS table names and can be removed completely since we are already printing out all the parsed arguments through print_args().

Signed-off-by: terrytangyuan terrytangyuan@gmail.com