Remove dead code: `packages_events` and related code

Proposal

The packages_events tables is not used and was a feature that was intended to track package-specific events that was abandoned in favor of a redis solution.

We should remove the relevant code (which I believe includes the :collect_package_events feature flag and then drop the packages_events table.

Note that the Packages::Event class is still in use, so it should not necessarily be entirely removed.