Remove unused/disabled source onion service info files

[rmol]

Status

Ready for review

Description of Changes

Fixes #5400.

If a site disables v2 onion services, remove the file used to decide to show the deprecation warning.

The v3 equivalent is also removed if v3 services are disabled, though downgrading to v2-only is not really possible -- more work would be needed in the playbooks, and that's probably not something we should support at this point.

Testing

• Start with a deployment that has v2 onion services enabled. VM or hardware is most straightforward at this point, but I'll see if it can be tested in a staging environment.
• Run securedrop-admin sdconfig to enable v3 and disable v2 onion services.
• Run securedrop-admin install. This should complete successfully, and in the Ansible output you should see Remove source v2 onion service info if not enabled followed by Expose source v3 onion service info to app.
• Log in to the app server and list the contents of /var/lib/securedrop. There should be no source_v2_url, just source_v3_url.
• Run securedrop-admin tailsconfig.
• Log in to the journalist interface. There should be no v2 deprecation warning.

Deployment

This enables admins to disable v2 onion services and remove the deprecation warning from the journalist interface.

Checklist

If you made changes to securedrop-admin:

• Linting and tests (make -C admin test) pass in the admin development container

If you made non-trivial code changes:

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

[zenmonkeykstop]

Test plan passes, LGTM!