Correct switched-around configuration descriptions for metamta.herald.show-hints and metamta.reply.show-hints

Summary: Fixes T3710. The text on these options is switched around.

Test Plan: {F54051} {F54052}

Reviewers: btrahan, nmalcolm, chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T3710

Differential Revision: https://secure.phabricator.com/D6737