Remove unused QObject parent arguments on options pages

In the new plugin setup scheme they are data members of the
plugin pimpl and never use the parent.

Change-Id: I28fe150393e8159064dcfbd113ce0320af50fd58
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/dialogs/externaltoolconfig.cpp

@@ -392,8 +392,7 @@ static void fillBaseEnvironmentComboBox(QComboBox *box)
         box->addItem(provider.displayName, Id::fromName(provider.id).toSetting());
 }
 
-ExternalToolConfig::ExternalToolConfig(QWidget *parent) :
-    QWidget(parent),
+ExternalToolConfig::ExternalToolConfig() :
     ui(new Ui::ExternalToolConfig),
     m_model(new ExternalToolModel(this))
 {