chore(httpx2): Remove transaction-based tracing

[sentrivana]

Same as httpx.

Closes https://linear.app/getsentry/issue/PY-2698/remove-transaction-based-tracing-from-httpx2

[linear-code]

PY-2698

[github-actions]

Codecov Results 📊

✅ 116770 passed | ⏭️ 5544 skipped | Total: 122314 | Pass Rate: 95.47% | Execution Time: 385m 32s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📉 -15381
Passed Tests	📉 -13815
Failed Tests	—
Skipped Tests	📉 -1566

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2255 uncovered lines.
✅ Project coverage is 90.46%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    90.24%    90.46%    +0.22%
==========================================
  Files          193       185        -8
  Lines        25715     23635     -2080
  Branches      9502      8688      -814
==========================================
+ Hits         23206     21380     -1826
- Misses        2509      2255      -254
- Partials      1435      1361       -74

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