Cleanup around trace/span model

[cbeauchesne]

Changes

• remove dead code
• mode get_rid from a raw function to a method os span classes

Workflow

1. ⚠️ Create your PR as draft ⚠️
2. Work on you PR until the CI passes
3. Mark it as ready for review
   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

🚀 Once your PR is reviewed and the CI green, you can merge it!

🛟 #apm-shared-testing 🛟

Reviewer checklist

• Anything but tests/ or manifests/ is modified ? I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added, removed or renamed?
  • Get a review from R&P team

[github-actions]

CODEOWNERS have been resolved as:

utils/dd_types/_utils.py                                                @DataDog/system-tests-core
docs/edit/add-new-test.md                                               @DataDog/system-tests-core
docs/internals/agent-interface-validation-methods.md                    @DataDog/system-tests-core
utils/dd_types/_datadog_agent_trace.py                                  @DataDog/system-tests-core
utils/dd_types/_datadog_library_trace.py                                @DataDog/system-tests-core
utils/interfaces/_agent.py                                              @DataDog/system-tests-core
utils/interfaces/_backend.py                                            @DataDog/system-tests-core
utils/interfaces/_core.py                                               @DataDog/system-tests-core
utils/interfaces/_library/core.py                                       @DataDog/system-tests-core
utils/interfaces/_test_agent.py                                         @DataDog/system-tests-core
utils/tools.py                                                          @DataDog/system-tests-core
utils/interfaces/_library/_utils.py                                     @DataDog/system-tests-core

[datadog-datadog-prod-us1-2]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

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