Don't put the entire corpus into project edit feed stories

Summary: Fixes T8723. We override timeline titles for these fields to shorten them, but the parent class shows full values for feed edits, which can lead to screen-sized notifications.

Test Plan: Edited a project, saw a reasonably-sized notification for it.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T8723

Differential Revision: https://secure.phabricator.com/D13485