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