drop etl temporarly

[rtroilo]

This PR drops the oshdb-etl module as it will be replaces by a newer version in upcoming PRs.

Checklist

• My code follows the code-style rules, and I have checked on the static analyses and benchmark (if applicable) results
• [ ] I have commented my code
• [ ] I have written javadoc (required for public classes and methods)
• [ ] I have added sufficient unit tests
• I have made corresponding changes to the documentation → Update documentation for 1.0 release #448
• I have updated the CHANGELOG.md
• I have adjusted the examples or created an issue in the corresponding repository
• I have adjusted the benchmark or created an issue in the corresponding repository

Please check all finished tasks. If some tasks do not apply to your PR, please cross their text out (by using ~...~) and remove their checkboxes.