revert(distributed_tracing): ensure last datadog parent id tag is always set

[mabdinur]

This reverts commit 2230214.

W3C-Datadog header specification has significant gaps and needs to be revised. This change is unreleased so a release note is not required.

Checklist

• Change(s) are motivated and described in the PR description
• Testing strategy is described if automated tests are not included in the PR
• Risks are described (performance impact, potential for breakage, maintainability)
• Change is maintainable (easy to change, telemetry, documentation)
• Library release note guidelines are followed or label changelog/no-changelog is set
• Documentation is included (in-code, generated user docs, public corp docs)
• Backport labels are set (if applicable)
• If this PR changes the public interface, I've notified @DataDog/apm-tees.

Reviewer Checklist

• Title is accurate
• All changes are related to the pull request's stated goal
• Description motivates each change
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Change is maintainable (easy to change, telemetry, documentation)
• Release note makes sense to a user of the library
• 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

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: revert-9174-munir/w3c-changes-2-3
Commit report: 2a1af83
Test service: dd-trace-py

✅ 0 Failed, 169168 Passed, 2269 Skipped, 9h 4m 12.33s Total duration (45m 4.54s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-05-13 20:53:26

Comparing candidate commit 2a1af83 in PR branch revert-9174-munir/w3c-changes-2-3 with baseline commit de5efd3 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 209 metrics, 9 unstable metrics.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 6.70%. Comparing base (de5efd3) to head (2a1af83).

Files	Patch %	Lines
ddtrace/propagation/http.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #9231       +/-   ##
===========================================
- Coverage   75.60%    6.70%   -68.91%     
===========================================
  Files        1283     1253       -30     
  Lines      120889   119107     -1782     
===========================================
- Hits        91403     7987    -83416     
- Misses      29486   111120    +81634     

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