ProjectExplorer: Change BuildStepConfigWidget::summaryWidget()

From a virtual function to a normal one backed by a real data member.

That's essentially what several re-implementations did, the other
ones used a fixed value instead.

Change-Id: I61e45f1d4f7f0f80fe2eb1f2729785f37e7bb803
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/autotoolsprojectmanager/configurestep.h

@@ -111,13 +111,10 @@ class ConfigureStepConfigWidget : public ProjectExplorer::BuildStepConfigWidget
 public:
     ConfigureStepConfigWidget(ConfigureStep *configureStep);
 
-    QString summaryText() const override;
-
 private:
     void updateDetails();
 
     ConfigureStep *m_configureStep;
-    QString m_summaryText;
     QLineEdit *m_additionalArguments;
 };