QmlOutline: Don't use LookupContext due to performance issues

Creating a LookupContext can be sloooow for large projects. We create
one instance for every update in the Outline to get the right icons.

Take a shortcut here and just use the element name directly, ignoring
packages names etc.

This is a hot fix for 2.1, a following patch will change the Icon
retrieval API accordingly.

Reviewed-by: Roberto Raggi
Task-number: QTCREATORBUG-2859

src/plugins/qmljseditor/qmloutlinemodel.h

@@ -120,7 +120,6 @@ private:
     QStandardItem *m_currentItem;
     QmlJS::Icons *m_icons;
 
-    QmlJS::LookupContext::Ptr m_context;
     QHash<QString, QIcon> m_typeToIcon;
     QHash<QmlOutlineItem*,QIcon> m_itemToIcon;
     QHash<QmlOutlineItem*,QmlJS::AST::Node*> m_itemToNode;