test: fix testing/integration tests to work with rumba

[LeoMcA]

• removed old paths and redirects
• removed behind_cdn check and assumed we always are

alerted to these broken tests by https://github.com/mdn/yari/pull/7887

outstanding issues:

1. headless/test_cdn.py::test_not_cached[/healthz-200-None] fails because we cache /healthz behind cloudfront - I suppose this doesn't matter, if we just use it within k8s, and we should remove the check?
2. we don't run this anywhere automatically, should I add a github action cronjob?

[LeoMcA]

@fiji-flo could you have a look at the github action before I merge?

[caugner]

Converted to draft, as several integration test cases are failing.