[SPARK-16371][SQL] Two follow-up tasks

## What changes were proposed in this pull request?
This is a small follow-up for SPARK-16371:

1. Hide removeMetadata from public API.
2. Add JIRA ticket number to test case name.

## How was this patch tested?
Updated a test comment.

Author: Reynold Xin <rxin@databricks.com>

Closes #14074 from rxin/parquet-filter.