Implement DestructibleInterface for Owners Packages

Summary:
Fixes T9945. This is straightforward.

The two sub-object types are very lightweight so I just deleted them directly instead of loading + delete()'ing (or implementing DestructibleInterface on them, which would require they have PHIDs).

Also improve a US English localization.

Test Plan:

• Used bin/remove destroy PHID-... --trace to destroy a package.
• Verified it was gone.
• Inspected the SQL in the log for general reasonableness.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9945

Differential Revision: https://secure.phabricator.com/D14729