(stable) Fix file attach bug in Macro

Summary: This was mis-tested by only using one account, which could always see the image. External transaction moved file attachment to the modular transaction for file and audio instead.

Test Plan: Test adding audio and a macro on a pleb account, visit with normal account and see macro fine.

Reviewers: epriestley, amckinley

Reviewed By: amckinley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17836