Improve some new string translations

Summary: Ref T2217. Cleans up some of the "attached %d file(s)" stuff.

Test Plan: Generated some of these transactions and verified they render more naturally.

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2217

Differential Revision: https://secure.phabricator.com/D7096