Skip loading file transform sources when we know a file is not transformed

Summary:
Depends on D19223. Ref T13106. When we're loading a file, we currently test if it's a transformed version of another file (usually, a thumbnail) and apply policy behavior if it is.

We know that builtins and profile images are never transforms and that the policy behavior for these files doesn't matter anyway. Skip loading transforms for these files.

Test Plan: Saw local queries drop from 146 to 139 with no change in behavior.

Maniphest Tasks: T13106

Differential Revision: https://secure.phabricator.com/D19224