Do not use QAbstractItemModel::reset().

Change-Id: Ie49bdf576a6d3543aef6df133b27c8827775c935
Rationale:
    a) It is conceptually cleaner to do the changes to the model
       in between calls to beginResetModel() and endResetModel,
       respectively.
    b) The function is deprecated in Qt 5, for exactly that reason.
Reviewed-by: hjk <qthjk@ovi.com>

src/plugins/debugger/sourcefileshandler.h

@@ -56,7 +56,6 @@ public:
     Qt::ItemFlags flags(const QModelIndex &index) const;
 
     void clearModel();
-    void update() { reset(); }
 
     void setSourceFiles(const QMap<QString, QString> &sourceFiles);
     void removeAll();