fix(pageserver): remove update_gc_info calls in tests

[skyzh]

Problem

introduced by #7468 conflicting with #7584

Summary of changes

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

2880 tests run: 2759 passed, 0 failed, 121 skipped (full report)

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Flaky tests (3)

Postgres 16

• test_gc_of_remote_layers: debug

Postgres 15

• test_tenant_delete_smoke: release

Postgres 14

• test_partial_evict_tenant[relative_spare]: release

Code coverage* (full report)

• functions: 31.4% (6224 of 19809 functions)
• lines: 47.2% (46681 of 98965 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
eb72b6e at 2024-05-03T16:09:27.256Z :recycle:}