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/Config/SettingsWindow.cpp

@@ -24,8 +24,6 @@
 
 StackedSettingsWindow::StackedSettingsWindow(QWidget* parent) : QDialog{parent}
 {
-  setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
-
   // This eliminates the ugly line between the title bar and window contents with KDE Plasma.
   setStyleSheet(QStringLiteral("QDialog { border: none; }"));