TextEditor: Flip default to 'duplicatedSupported'

opt-out now, for all editors created by BaseTextEditorFactories.

Change-Id: I01d0a9ff26320fcd0b84ff90ff22c747cf84b84c
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/glsleditor/glsleditor.cpp

@@ -335,7 +335,6 @@ class GlslEditor : public TextEditor::BaseTextEditor
 public:
     GlslEditor()
     {
-        setDuplicateSupported(true);
     }
 
     bool open(QString *errorString, const QString &fileName, const QString &realFileName)