ref: Drop hub related code in new major

[sentrivana]

Description

Remove everything hub related, including all sorts of compatibility shims around hubs/scopes.

Also remove deprecated session methods.

configure_scope and push_scope removal coming in a future PR.

Issues

Closes #5001

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 📊

✅ 98261 passed | ⏭️ 6731 skipped | Total: 104992 | Pass Rate: 93.59% | Execution Time: 357m 13s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📉 -322
Passed Tests	📉 -297
Failed Tests	—
Skipped Tests	📉 -25

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2487 uncovered lines.
❌ Project coverage is 89.74%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
- Coverage    89.84%    89.74%     -0.1%
==========================================
  Files          193       192        -1
  Lines        24588     24239      -349
  Branches      8744      8620      -124
==========================================
+ Hits         22089     21752      -337
- Misses        2499      2487       -12
- Partials      1400      1391        -9

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