We should remove Wikibase\Client\Usage\SiteLinkUsageLookup if it's no longer needed.
It is not used in the current code anywhere as it was replaced by SqlUsageTracker, but @daniel raised concerns over the potential future usage in other contexts.
It is currently only used in AffectedPagesFinderTest.php (and tests for itself).
The usage here could likely be replaced by something simpler / a mock / a different implementation.
Task
Evaluate if this class can be removed and mocks used, or if the mocks would be too complicated and thus the class should remain.