Don't repeat the diff property table when clicking "show more"

Summary:
If you "chmod +x" a file and then generate a diff and click "show 20 lines" on
that diff, you get another janky copy of the property table. Render the property
table only for top-level rendering requests.

This started happening after D409, which fixed the far-more-obvious bug of these
things never showing up. We must have changed the logic at some point since this
side effect was surprising to me. :P

Test Plan:
Created a diff with changes and +x, clicked "show 20 lines".

• Original diff had file property header table thing, showing the +x.
• New context brought in by "show 20 lines" didn't have it anymore.

Reviewed By: jungejason
Reviewers: aran, jungejason, tuomaspelkonen
CC: aran, epriestley, jungejason
Differential Revision: 482