Remove unnecessary objectmapper from ParquetMetadata

[asfimport]

Reporter: Nezih Yigitbasi / @nezihyigitbasi
Assignee: Nezih Yigitbasi / @nezihyigitbasi

Related issues:

• Release Parquet-mr 1.9.0 (blocks)

PRs and other links:

• PR 227

_{Note: This issue was originally created as PARQUET-318. Please see the migration documentation for further details.}

[asfimport]

Ryan Blue / @rdblue:
Merged #227. Thanks, Nezih!