Remove buildable handle / container handle logic form Harbormaster buildable queries

Summary:
Ref T10457. We currently have these weird, out-of-place methods on Harbormaster queries that just load handles. These were written before HandlePool, and HandlePool is now more convenient, simpler, and more efficient.

Drop this stuff in favor of using handle pools off $viewer.

Test Plan: Looked at buildable list, looked at buildable detail, grepped for removed methods.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10457

Differential Revision: https://secure.phabricator.com/D15354