[SPARK-13518][SQL] Enable vectorized parquet scanner by default

## What changes were proposed in this pull request?

Change the default of the flag to enable this feature now that the implementation is complete.

## How was this patch tested?

The new parquet reader should be a drop in, so will be exercised by the existing tests.

Author: Nong Li <nong@databricks.com>

Closes #11397 from nongli/spark-13518.