Removed unused buildApplicationPage method from PhabricatorController

Summary: Getting rid of some code! This method has no callsites so it should be safe to remove completely. Ref T9690

Test Plan: Removed method and clicked around to make sure nothing broke.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: yelirekim, epriestley

Maniphest Tasks: T9690

Differential Revision: https://secure.phabricator.com/D16439