refactor(pageserver): remove --update-init flag

[problame]

We don't actually use it.

refs #7555

[github-actions]

2928 tests run: 2807 passed, 0 failed, 121 skipped (full report)

---

Flaky tests (6)

Postgres 15

• test_partial_evict_tenant[relative_equal]: release
• test_storage_controller_smoke: release
• test_delete_tenant_exercise_crash_safety_failpoints[real_s3-tenant-delete-before-cleanup-remaining-fs-traces-False-Check.RETRY_WITHOUT_RESTART]: release
• test_delete_tenant_exercise_crash_safety_failpoints[real_s3-tenant-delete-before-remove-tenant-dir-False-Check.RETRY_WITH_RESTART]: release
• test_delete_tenant_exercise_crash_safety_failpoints[real_s3-timeline-delete-before-rm-False-Check.RETRY_WITH_RESTART]: release

Postgres 14

• test_vm_bit_clear_on_heap_lock: debug

Code coverage* (full report)

• functions: 31.4% (6228 of 19841 functions)
• lines: 47.1% (46692 of 99065 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
a52b563 at 2024-05-04T16:33:08.544Z :recycle:}