QmlDesigner: fix crash on mac

Came from two deletions at the same time QCache::remove and
delete on sharedMemory.QmlDesigner:

Change-Id: I6a29cf160c8e81ecd955cf36999edc639fbbb63f
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

share/qtcreator/qml/qmlpuppet/container/imagecontainer.cpp

@@ -121,7 +121,6 @@ static SharedMemory *createSharedMemory(qint32 key, int byteCount)
 
         if (!sharedMemory->isAttached()) {
             globalSharedMemoryContainer()->remove(key);
-            delete sharedMemory;
             sharedMemory = 0;
         }
     }