Fixed SimpleCocoaVTK Xcode project to build properly.

- fix library names to use 6.2 in the filename
- In the xcconfig, don't assue VTK_USE_SYSTEM_ZLIB was
  used since the Read Me doesn't say it's required

Change-Id: Iddcc27678fcd9abf50db9c97ff308ec69529b125
Merge topic 'SimpleCocoaVTKTweaks' into master

553c12ea Fixed SimpleCocoaVTK Xcode project to build properly.