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/Settings/BroadbandAdapterSettingsDialog.cpp

@@ -95,7 +95,6 @@ void BroadbandAdapterSettingsDialog::InitControls()
   }
 
   setWindowTitle(window_title);
-  setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
 
   m_address_input = new QLineEdit(current_address);
   m_address_input->setPlaceholderText(address_placeholder);