Removed unused validateNavigationMenuItem() from PhabricatorProfileMenuEngine

Summary:
The commit rP7bde92b9c9806c5967df617fb4e843dea315ecf7 (2016) introduced `private function validateNavigationMenuItem()`.
The only call to this method was removed in rP950e9d085b482bc3484e2066591ac07c20154c9a.
Thus remove this unused method.

Test Plan:
Read/grep the code in `PhabricatorProfileMenuEngine`.

Run also `grep -RF 'validateNavigationMenuItem' --include="*.php" .` to verify that this is an orphan method.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Differential Revision: https://we.phorge.it/D25719

src/applications/search/engine/PhabricatorProfileMenuEngine.php

@@ -469,15 +469,6 @@ abstract class PhabricatorProfileMenuEngine extends Phobject {
     return $map;
   }
 
-  private function validateNavigationMenuItem($item) {
-    if (!($item instanceof PHUIListItemView)) {
-      throw new Exception(
-        pht(
-          'Expected buildNavigationMenuItems() to return a list of '.
-          'PHUIListItemView objects, but got a surprise.'));
-    }
-  }
-
   public function getConfigureURI() {
     $mode = $this->getEditMode();