[Redesign] Minor CSS polish in Feed Story

Summary: Ref T8099, Remove final border, break words in titles.

Test Plan: See line vanish before my eyes!

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8099

Differential Revision: https://secure.phabricator.com/D13491