When a user tries to regsiter while logged in, just send them home

Summary: This error message is pointless and dead-ends logged-in users needlessly if they're sent to the register page by documentation or Advanced Enterprise Sales Funnels.

Test Plan: Visited `/auth/register/` while logged in, was sent home.

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D15739

src/applications/auth/controller/PhabricatorAuthRegisterController.php

@@ -12,7 +12,7 @@ final class PhabricatorAuthRegisterController
     $account_key = $request->getURIData('akey');
 
     if ($request->getUser()->isLoggedIn()) {
-      return $this->renderError(pht('You are already logged in.'));
+      return id(new AphrontRedirectResponse())->setURI('/');
     }
 
     $is_setup = false;