Remove limit from helpfulness votes.

[alice-blue]

In the PR for the mod recent activity tool (#1284), I wrote

The limit on the reviewvotes query (currently in line 211)
ORDER BY reviewvotes.createdate DESC LIMIT 100', [$recent_days]);
exists only because of #1286. The limit should probably be removed after the createdate column in the reviewvotes table gets sorted out.

The dates in the createdate column are no longer presenting a problem, so this PR removes that limit.