R1:78e36d6b17a5

Implement DestructibleInterface on GitLFS refs

Summary: Ref T7789. Make sure these get cleaned up when a repository is destroyed.

Test Plan:
- Created a new repository.
- Pushed some LFS data to it.
- Used `bin/remove destroy` to nuke it.
- Verified the LFS stuff was cleaned up and the underlying files were destroyed (`SELECT * FROM repository_gitlfsref`, etc).

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T7789

Differential Revision: https://secure.phabricator.com/D15493