Removes db/fixtures from database files

What does this MR do?

It was discussed at Database Office hours that it's not necessary to suggest a database review for the files in db/fixtures, since they are only used in development.

Database Office hours document: https://docs.google.com/document/d/1wgfmVL30F8SdMg-9yY6Y8djPSxWNvKmhR5XmsvYX1EI/edit#

This MR removes those files from Danger

cc @abrandl

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• [-] 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