R1:6d5c9e897d31

Hide "Revision" column in Diffusion history view if Differential is uninstalled

Summary: Fixes T9481. If the viewer does not have access to Differential (for example, because it is not installed), hide the "Revision" column in Diffusion.

Test Plan:
- Viewed history, saw "Revision" column.
- Uninstalled Differential, reloaded, no "Revision" column.

Reviewers: chad

Reviewed By: chad

Subscribers: revi

Maniphest Tasks: T9481

Differential Revision: https://secure.phabricator.com/D14188