Summary:
Ref T8095.
Harbormaster has a `BuildItem` class, but it has no table and is unused. This was an earlier idea about representing lint/unit results and some other possible types of messages, but I think we want to be more specific than this.
Remove `BuildItem` and add `Lint` and `Unit` storage. These tables roughly parallel how we store lint/unit messages today, with some guesses about how where they'll go in the future.
Test Plan: Ran `bin/storage upgrade` and got a clean adjust out of it.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: hach-que, epriestley
Maniphest Tasks: T8095
Differential Revision: https://secure.phabricator.com/D13329
