DolphinQt: Kill some unused member variables.

Source/Core/DolphinQt/Config/Mapping/MappingWidget.cpp

@@ -121,8 +121,6 @@ QGroupBox* MappingWidget::CreateGroupBox(const QString& name, ControllerEmu::Con
     const QString translated_name =
         translate ? tr(control->ui_name.c_str()) : QString::fromStdString(control->ui_name);
     form_layout->addRow(translated_name, button);
-
-    m_buttons.push_back(button);
   }
 
   for (auto& setting : group->numeric_settings)

Source/Core/DolphinQt/Config/Mapping/MappingWidget.h

@@ -60,6 +60,4 @@ protected:
 
 private:
   MappingWindow* m_parent;
-  bool m_first = true;
-  std::vector<MappingButton*> m_buttons;
 };