Allow pastes to be destroyed

Summary: Fixes T6186.

Test Plan:
  - Used `bin/remove destroy Pxxx` to destroy a paste.
  - Verified file, transactions, etc., were destroyed.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T6186

Differential Revision: https://secure.phabricator.com/D10563