Don't set focused to nullptr when opening new UI dialogs

This messes up custom focusing logic (e.g. when you open certain window
and manually set focus). CUIFocusSystem::Update will deal with cleanup
otherwise.

src/xrGame/UIDialogHolder.cpp

@@ -55,7 +55,6 @@ void CDialogHolder::StartMenu(CUIDialogWnd* pDialog, bool bDoHideIndicators)
             CurrentGameUI()->ShowGameIndicators(false);
         }
     }
-    UI().Focus().SetFocused(nullptr);
     pDialog->SetHolder(this);
 
     if (pDialog->NeedCursor())