ref(langchain): Remove on_agent_finish() hook

[alexander-alderman-webb]

Description

There is no hook that stores a span corresponding to the run_id.

Issues

Reminders

• Please add tests to validate your changes, and lint your code using uv run ruff.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[github-actions]

Codecov Results 📊

✅ 99162 passed | ⏭️ 6479 skipped | Total: 105641 | Pass Rate: 93.87% | Execution Time: 357m 51s

📊 Comparison with Base Branch

Metric	Change
Total Tests	—
Passed Tests	📈 +1
Failed Tests	📉 -1
Skipped Tests	—

➖ Removed Tests (1)

View removed tests

• test_continuous_profiler_auto_start_and_stop_sampled[experiment-gevent]
  • File: tests.profiler.test_continuous_profiler

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2502 uncovered lines.
✅ Project coverage is 89.97%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    89.95%    89.97%    +0.02%
==========================================
  Files          193       193         —
  Lines        24955     24946        -9
  Branches      9004      9000        -4
==========================================
+ Hits         22448     22444        -4
- Misses        2507      2502        -5
- Partials      1437      1435        -2

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