Fix Diffusion blame columns when disabling blame

Summary:
Fixes T10385. Two issues:

• $show_blame and $show_color were improperly swapped.
• Code to hide these columns got dropped somewhere, probably in my recent-ish rewrite.

Test Plan:

• Showed/hid blame.
• Showed/hid colors.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10385

Differential Revision: https://secure.phabricator.com/D15528