Rename "needReviewerStatus()" into "needReviewers()"

Summary: Ref T10967. The old name was because we had a getReviewers() tied to needRelationships(), rename this method to use a simpler and more clear name.

Test Plan: grep, browsed around.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10967

Differential Revision: https://secure.phabricator.com/D17519