Use Remarkup in linter messages
Summary: Use Remarkup (specifically, backticks) within linter messages. Depends on D14485.
Test Plan: Eyeball it.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D14489