Fix fatal in rendering Phriction "Moved Away" stories

Summary:
Ref T13202. See PHI881. These stories have bad rendering methods, but they didn't previously render into the timeilne (since Phriction documents didn't have a timeline).

Update the rendering to work.

The rendered outcome isn't great (it isn't very clear or explicit about exactly what moved where), but I'll fix that in a followup. This is a net improvement since it doesn't fatal the page, at least.

Test Plan:

• Moved page "X" to "Y".
• Viewed the old page "X".
• Before patch: bad timeline story would fatal rendering.
• After patch: story renders, at least, just not great.

Reviewers: amckinley

Maniphest Tasks: T13202

Differential Revision: https://secure.phabricator.com/D19682