pageserver: downgrade ephemeral layer roll wait message

[erikgrinaker]

We already log a message for this during the L0 flush, so the additional message is mostly noise.

[github-actions]

7557 tests run: 7182 passed, 0 failed, 375 skipped (full report)

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Flaky tests (1)

Postgres 17

• test_large_records: release-arm64-without-lfc

Code coverage* (full report)

• functions: 32.9% (8621 of 26200 functions)
• lines: 48.8% (72721 of 148909 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
66ff275 at 2025-02-20T12:16:25.048Z :recycle:}