Don't apply inline rules in Literal remarkup blocks

Summary:
  - Long ago, we applied HTML escaping in literal block rules (`%%% .. %%%`) by using an HTML inline rule.
    - We no longer need to do this, so literal blocks don't need to apply inline rules at all.
  - I think I imagined that certain block rules might want nonstandard inline rules when building Remarkup originally.
    - They never do and we don't have any use cases on the horizon where they might.

This allows us to simplify remarkup code in Phabricator.

Test Plan: Typed `%%% <strong>!!</strong> %%%` into Remarkup and made sure it was still escaped properly.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6395