Update one straggling "CAN_INTERACT" check in comment removal

Summary: See rPaacc62463d61. D20551 added some CAN_INTERACT checks, but CAN_INTERACT needs to be checked with canInteract() to fall back to CAN_VIEW properly. D20558 cleaned up most of this but missed one callsite; fix that up too.

Test Plan: Removed a comment on a commit.

Reviewers: amckinley, 20after4

Reviewed By: amckinley

Differential Revision: https://secure.phabricator.com/D20648