Fix weird remarkup linewrapping on a few instructions forms, plus move toward fixing Phame/CORGI remarkup issues

Summary:
Fixes T10381. When we converted to PHUIRemarkupView, some instructional text got linebreaks added when it shouldn't have them (the source is written in PHP and wrapped at 80 characters, but the output should flow naturally).

Fix this so we don't preserve linebreaks.

This also makes PHUIRemarkupView a little more powerful and inches us toward fixing Phame/CORGI remarkup issues, getting rid of PhabricatorMarkupInterface / PhabricatorMarkupOneOff, and dropping all the application hard-coding in PhabricatorMarkupEngine.

Test Plan:

• Grepped for all callsites, looking for callsites which accept remarkup written in <<<HEREDOC format.
• Viewed form instructions, Conduit API methods, HTTP parameter edit instructions.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10381

Differential Revision: https://secure.phabricator.com/D15963