DiffEditorManager simplify

by using EditorManager::openEditorWithContents

Change-Id: I2850648bff0f5b8f01254b9c7ce9539c1262f576
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/diffeditor/diffeditordocument.h

@@ -49,7 +49,6 @@ class DiffEditorDocument : public Core::BaseTextDocument
     Q_PROPERTY(QString plainText READ plainText STORED false) // For access by code pasters
 public:
     DiffEditorDocument();
-    ~DiffEditorDocument();
 
     DiffEditorController *controller() const;