Help: Do not save settings in help database

Using the help database is not necessary, does not follow our style,
and is less reliable (with all the setupEngine mess).

Change-Id: Icb7f63a6b349458011e1b068bdf0954b78d3281f
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/help/generalsettingspage.h

@@ -54,7 +54,6 @@ public:
 
 signals:
     void fontChanged();
-    void returnOnCloseChanged();
 
 private slots:
     void setCurrentPage();