Editors: Provide a base implementation for duplicate{,Supported}

Helps avoiding trivial re-implementations.

Change-Id: Iaa2e6b92503a2b9553432568c2047c28899c7ea6
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/diffeditor/diffeditoreditable.cpp

@@ -98,17 +98,6 @@ void DiffEditorEditable::setDisplayName(const QString &title)
     emit changed();
 }
 
-bool DiffEditorEditable::duplicateSupported() const
-{
-    return false;
-}
-
-Core::IEditor *DiffEditorEditable::duplicate(QWidget *parent)
-{
-    Q_UNUSED(parent)
-    return 0;
-}
-
 Core::Id DiffEditorEditable::id() const
 {
     return Constants::DIFF_EDITOR_ID;