ref(mcp): Remove redundant mcp.tool.result.is_error

[alexander-alderman-webb]

Description

The attribute is redundant with the captured exception, and is deprecated anyway.

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 📊

✅ 98542 passed | ⏭️ 6772 skipped | Total: 105314 | Pass Rate: 93.57% | Execution Time: 355m 23s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📈 +32
Passed Tests	📈 +32
Failed Tests	📉 -1
Skipped Tests	📈 +1

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2499 uncovered lines.
✅ Project coverage is 89.84%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    89.84%    89.84%        —%
==========================================
  Files          193       193         —
  Lines        24588     24587        -1
  Branches      8744      8744         —
==========================================
+ Hits         22089     22088        -1
- Misses        2499      2499         —
- Partials      1400      1400         —

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