Debian routes consistency

What does this MR do?

See gitlab-workhorse#343 (closed)

This removes the /- portion of the project level routes for consistency with the other package APIs. We want to have a consistent route prefix because we have special rate limiting in place for the package APIs based on this prefix to be able to handle a larger number of requests than the rest of the API.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry (not needed, API is behind a feature flag)
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability 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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team