Doc: Remove broken link from iOS documentation

The wiki page containing the example as referred to in the
docs has been removed.

The example code has been tracked down and will get pushed as
a proper example in a separate commit. This page will be updated
accordingly when the example is there.

Task-number: QTBUG-55651
Change-Id: Ie25b7a6ebfe7a022bb02f3ceee9fce3c8a7326af
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

doc/src/platforms/apple-getting-started.qdocinc

@@ -100,8 +100,5 @@
     Most useful is perhaps the possibility for adding In-App
     Purchasing with the StoreKit framework.
 
-    We currently have one example mixing Objective-C and C++ code. You
-    find it
-    \l{http://wiki.qt.io/Mixing_C_and_ObjectiveC_Code}{here}.
 //! [getting started]
 */