[SPARK-19065][SQL] Don't inherit expression id in dropDuplicates

## What changes were proposed in this pull request?

`dropDuplicates` will create an Alias using the same exprId, so `StreamExecution` should also replace Alias if necessary.

## How was this patch tested?

test("SPARK-19065: dropDuplicates should not create expressions using the same id")

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #16564 from zsxwing/SPARK-19065.