Update obsolete max face count debug log to use newer API

Assets/Scenes/FaceTracking/DisplayFaceInfo.cs

         if (m_FaceManager.subsystem != null && faceInfoText != null)
         {
             faceInfoText.text = $"Supported number of tracked faces: {m_FaceManager.supportedFaceCount}\n" +
-                                $"Max number of faces to track: {m_FaceManager.maximumFaceCount}\n" +
+                                $"Max number of faces to track: {m_FaceManager.currentMaximumFaceCount}\n" +
                                 $"Number of tracked faces: {m_FaceManager.trackables.count}";
         }
     }