[SPARK-19409][SPARK-17213] Cleanup Parquet workarounds/hacks due to bugs of old Parquet versions

## What changes were proposed in this pull request?

We've already upgraded parquet-mr to 1.8.2. This PR does some further cleanup by removing a workaround of PARQUET-686 and a hack due to PARQUET-363 and PARQUET-278. All three Parquet issues are fixed in parquet-mr 1.8.2.

## How was this patch tested?

Existing unit tests.

Author: Cheng Lian <lian@databricks.com>

Closes #16791 from liancheng/parquet-1.8.2-cleanup.