Remove nonfunctional links from Differential inline comment previews

Summary:
They currently have "Next", "Previous" and "Reply" links which don't work. Don't
render these links.

Test Plan:
Looked at inline previews, didn't see any silly/nonfunctional links.

Reviewed By: tuomaspelkonen
Reviewers: aran, jungejason, tuomaspelkonen
CC: aran, epriestley, tuomaspelkonen
Differential Revision: 419