Switch File deletion to use ModularTransactions

Summary: Fixes T12587. Adds a new PhabricatorFileDeleteTransaction that enqueues File delete tasks.

Test Plan:

• hack PhabricatorFileQuery to ignore isDeleted state
• stop daemons
• upload a file, delete it from the UI
• check that the DB has updated isDeleted = 1
• check timeline rendering in File detail view
• start daemons
• confirm rows are deleted from DB

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, thoughtpolice

Maniphest Tasks: T12587

Differential Revision: https://secure.phabricator.com/D17723