DolphinQt: Remove redundant window hints

Remove window hints clearing the flag Qt::WindowContextHelpButtonHint,
which is already off by default in Qt 6.

In Qt 5 this flag was set by default for QDialogs, and on Windows put a
? button in the corner of the title bar allowing users to activate Qt's
QWhatsThis help system for a given widget. Since we don't set that text
the ? button was useless and so we hid it manually.

Source/Core/DolphinQt/NetPlay/NetPlayDialog.cpp

@@ -97,8 +97,6 @@ NetPlayDialog::NetPlayDialog(const GameListModel& game_list_model,
     : QDialog(parent), m_game_list_model(game_list_model),
       m_start_game_callback(std::move(start_game_callback))
 {
-  setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
-
   setWindowTitle(tr("NetPlay"));
   setWindowIcon(Resources::GetAppIcon());