R1:6fea5e5ce7d5

Do not extract file PHIDs from remarkup blocks for attachment

Summary: Ref T13603. When processing transactions that include remarkup blocks, stop extracting file references from them for attachment.

Test Plan: Submitted a remarkup block with a file reference, no longer saw automatic file attachment.

Maniphest Tasks: T13603

Differential Revision: https://secure.phabricator.com/D21812