Remove all "ObjectHasFile" edge reads and writes
Summary: Ref T13603. Migrate all code which interacts with the "ObjectHasFile" edge to use the "Attachments" table instead.
- Edited a paste's view policy, confirmed associated file secret was scrambled.
- Verified I could still view paste content as a user who could not naturally view the underlying file.
Maniphest Tasks: T13603
Differential Revision: https://secure.phabricator.com/D21819