DiffEditor: Merge the two construction paths

Change-Id: I3c0c750517c9000dffe13de724b063008fd426b7
Reviewed-by: Christian Stenger <christian.stenger@digia.com>

src/plugins/diffeditor/diffeditor.h

@@ -55,10 +55,10 @@ class UnifiedDiffEditorWidget;
 class DIFFEDITOR_EXPORT DiffEditor : public Core::IEditor
 {
     Q_OBJECT
+
 public:
-    DiffEditor();
-    DiffEditor(DiffEditor *other);
-    virtual ~DiffEditor();
+    DiffEditor(const QSharedPointer<DiffEditorDocument> &doc);
+    ~DiffEditor();
 
 public:
     DiffEditorController *controller() const;
@@ -86,7 +86,6 @@ private slots:
     void slotDiffEditorSwitched();
 
 private:
-    void ctor();
     void updateEntryToolTip();
     void showDiffEditor(QWidget *newEditor);
     void updateDiffEditorSwitcher();