Removes database.yml.example

What does this MR do?

Removes database.yml.example

It's an empty file that was committed by accident on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28565

🤦

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Performance and testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers