Remove legacy pre-loading of handles from Herald rendering

Summary: Ref T13480. When Herald renders rules, it partly uses a very old handle pre-loading mechanism where PHIDs are extracted and loaded upfront. This was obsoleted a long time ago and was pretty shaky even when it worked. Get rid of it to simplify the code a little.

Test Plan: Viewed Herald rules rendered into static text with PHID list actions, saw handles. Grepped for all affected methods.

Maniphest Tasks: T13480

Differential Revision: https://secure.phabricator.com/D20948