CompilerExplorer: Remove unused member

Change-Id: I7cbab5db00d79c52f5fe4b78f9e6b5f1f382ba5a
Reviewed-by: hjk <hjk@qt.io>

src/plugins/compilerexplorer/compilerexplorereditor.cpp

@@ -178,7 +178,6 @@ signals:
 private:
     mutable CompilerExplorerSettings m_ceSettings;
     std::function<Utils::Store()> m_windowStateCallback;
-    QUndoStack *m_undoStack;
 };
 
 class SourceEditorWidget : public QWidget
@@ -372,7 +371,6 @@ public:
 };
 
 JsonSettingsDocument::JsonSettingsDocument(QUndoStack *undoStack)
-    : m_undoStack(undoStack)
 {
     setId(Constants::CE_EDITOR_ID);
     setMimeType("application/compiler-explorer");