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.

Test Plan:

• 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.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13603

Differential Revision: https://secure.phabricator.com/D21819