Clean up some custom field strings in Feed

Summary: Fixes T9919. We were missing feed strings and US English localizations for some of this stuff.

Test Plan:
Before:

{F1018877}

After:

{F1018879}
{F1018880}
{F1018881}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9919

Differential Revision: https://secure.phabricator.com/D14721