R1:f01c2e36948b

Remove "Large Changes" documentation and make some minor behavioral improvements

Summary:
Depends on D19296. Ref T13110.

- Remove the "Large Changesets" documentation since we now degrade very large changesets and I don't have any evidence that anyone has ever tried to follow any of the recommendations in this document.
- Remove references to it.
- When an older revision doesn't have denormalized size information on the Revision object itself, don't render a scale element (instead of rendering a…