DiffEditor: refactor internal structures.

Simplify the implementation a lot.

Change-Id: I3f5daa3d2ce14c28d48c2e1e996ec4935d1dae3f
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>

src/plugins/diffeditor/diffeditorplugin.h

@@ -53,10 +53,6 @@ public:
 private slots:
     void diff();
 
-#ifdef WITH_TESTS
-    void testFixPositions();
-#endif // WITH_TESTS
-
 private:
     QString getFileContents(const QString &fileName) const;