Delay database creation during setup

What does this Merge Request do?

No longer creates the development and test databases before running the usual dev:setup rake task.

There is logic in the GitLab codebase that assumes that if the database exists its schema will also be present, and booting the app with an empty database causes errors.

The dev:setup task will also set up a database, so this change should have no impact.

Original discussion in gitlab!24679 (comment 287317540)

Closes #806 (closed)

Merge Request checklist

• [-] Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• [-] Documentation added/updated, if needed.
• [-] gdk doctor test added, if needed.