Revert "fix(tracing): only extract distributed headers if a trace is not already started"

[brettlangdon]

Reverts #9456

This PR was merged automatically even though there was a failing system test. https://github.com/DataDog/dd-trace-py/actions/runs/12836948874/job/35799900676

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/contrib/trace_utils.py                                          @DataDog/apm-core-python @DataDog/apm-idm-python
ddtrace/settings/config.py                                              @DataDog/python-guild @DataDog/apm-sdk-api-python
tests/contrib/wsgi/test_wsgi.py                                         @DataDog/apm-core-python @DataDog/apm-idm-python
tests/utils.py                                                          @DataDog/python-guild

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: revert-9456-brettlangdon/fix.extra.distributed.extract
Commit report: 1809698
Test service: dd-trace-py

✅ 0 Failed, 1048 Passed, 550 Skipped, 17m 10.77s Total duration (22m 14.15s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-21 14:12:58

Comparing candidate commit 1809698 in PR branch revert-9456-brettlangdon/fix.extra.distributed.extract with baseline commit 731be65 in branch main.

Found 0 performance improvements and 3 performance regressions! Performance is the same for 391 metrics, 2 unstable metrics.

scenario:flasksqli-appsec-enabled

• 🟥 execution_time [+156.594µs; +166.028µs] or [+7.250%; +7.686%]

scenario:flasksqli-iast-enabled

• 🟥 execution_time [+158.052µs; +167.485µs] or [+7.320%; +7.757%]

scenario:flasksqli-tracer-enabled

• 🟥 execution_time [+162.724µs; +172.811µs] or [+7.579%; +8.049%]