[SPARK-10957] [ML] setParams changes quantileProbabilities unexpectly in PySpark's AFTSurvivalRegression

If user doesn't specify `quantileProbs` in `setParams`, it will get reset to the default value. We don't need special handling here. vectorijk yanboliang

Author: Xiangrui Meng <meng@databricks.com>

Closes #9001 from mengxr/SPARK-10957.