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/QtUtils/ParallelProgressDialog.h

@@ -26,7 +26,6 @@ public:
   ParallelProgressDialog(Args&&... args) : m_dialog{std::forward<Args>(args)...}
   {
     setParent(m_dialog.parent());
-    m_dialog.setWindowFlags(m_dialog.windowFlags() & ~Qt::WindowContextHelpButtonHint);
     ConnectSignalsAndSlots();
   }