Remove unused legacy Beam utils
_The documentation is not available anymore as the PR was closed or merged._
This PR removes unused legacy custom `WriteToParquet`, once official Apache Beam includes the patch since version 2.22.0: 
- Patch PR: https://github.com/apache/beam/pull/11699
- Issue: https://issues.apache.org/jira/browse/BEAM-10022

In relation with:
- #204