Allow max attribution rate limit when replacing an event report

[giladbarkan-github]

Resolves issue https://github.com/WICG/attribution-reporting-api/issues/1309

In step 15 of https://wicg.github.io/attribution-reporting-api/#trigger-event-level-attribution, we exit early if the number of persisted attribution rate limit records is equal to the max allowed; which means we reach step 17, replacing event-level reports, only if the number of persisted attribution rate limit records is less than the max allowed, even though we keep the number of attribution rate limit records in line with the number of reports by removing attribution rate limit records (step 12 of https://wicg.github.io/attribution-reporting-api/#maybe-replace-event-level-report).

Since having (max-1) persisted attribution rate limit records results in report replacements unlimited by max attributions per rate-limit window, it seems arbitrary to limit such report replacements when we keep max persisted attribution rate limit records.

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[linnan-github]

@pasin30055 Could you PTAL, thanks!