Fix "edit multiple reviewers" string

Summary:
Fixes T6543. This was slightly trickier than I thought.

The actual inputs to this are: author, total affected count, added count, added list, removed count, removed list.

We weren't accounting for "total affected count" (used to select the correct word for "reviewers", e.g. "reviewers-few" vs "reviewers-many").

Test Plan:

Reviewers: chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T6543

Differential Revision: https://secure.phabricator.com/D10846