Fix resource memory leak related to PreparedStatements

We noticed our server had a new memory leak after updating several plugins over the holidays. Using a profiling/leak detection tool, I finally tracked it down to LogBlock. New LogBlock code introduced PreparedStatements but was never closing them. This pull fixes that issue.

Although as the comment in the PR notes, I assume the PreparedStatements were introduced for perceived performance gains and that's not happening either as it stands today. But with this change, at least they aren't leaking memory on every insert either.