mpOwnMenu is unused since menubuttons stopped getting loaded from .res files

Change-Id: I11a1ff3d5427156c9d8485dd9294782459c11f8c

include/vcl/menubtn.hxx

@@ -36,7 +36,6 @@ private:
     friend class VclBuilder;
 
     Timer*          mpMenuTimer;
-    VclPtr<PopupMenu> mpOwnMenu;
     VclPtr<PopupMenu> mpMenu;
     sal_uInt16      mnCurItemId;
     sal_uInt16      mnMenuMode;

vcl/source/control/menubtn.cxx

@@ -32,7 +32,6 @@ void MenuButton::ImplInitMenuButtonData()
 
     mpMenuTimer     = nullptr;
     mpMenu          = nullptr;
-    mpOwnMenu       = nullptr;
     mnCurItemId     = 0;
     mnMenuMode      = 0;
 }
@@ -88,7 +87,6 @@ MenuButton::~MenuButton()
 void MenuButton::dispose()
 {
     delete mpMenuTimer;
-    mpOwnMenu.disposeAndClear();
     PushButton::dispose();
 }