removes 'source_v2_url' field from SI metadata endpoint

[zenmonkeykstop]

Status

Ready for review

Description of Changes

Super-closes #5731

Removes the v2 source URL from the Source Interface /metadata endpoint.

Testing

Dev

• run make dev and visit http://localhost:8080/metadata
  • verify that the v2_source_url field is not present
  • verify that the v3_source_url field is present with a null value
• log into the docker container with docker exec -it securedrop-dev-0 bash
• create a file /var/lib/securedrop/source_v3_url containing a valid v3 address (56-char.onion, no protocol)
• create a file /var/lib/securedrop/source_v2_url containing a valid v2 address (16-char.onion no protocol)
• visit http://localhost:8080/metadata
  • verify that the v2_source_url field is not present
  • verify that the v3_source_url field is present with the value from the source_v3_url file.

Deployment

Deployed with app-code .deb install/upgrade.

Checklist

If you made changes to the server application code:

• Linting (make lint) and tests (make test) pass in the development container

If you added or removed a file deployed with the application:

• I have updated AppArmor rules to include the change

If you made non-trivial code changes:

• I have written a test plan and validated it for this PR

Choose one of the following:

• I have opened a PR in the docs repo for these changes, or will do so later
• I would appreciate help with the documentation
• These changes do not require documentation

[conorsch]

Works beautifully. Thanks, @zenmonkeykstop.

Super-closes #5731

❤️ 😎