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/DiscordJoinRequestDialog.cpp

@@ -21,7 +21,6 @@ DiscordJoinRequestDialog::DiscordJoinRequestDialog(QWidget* parent, const std::s
     : QDialog(parent), m_user_id(id), m_close_timestamp(std::time(nullptr) + s_max_lifetime_seconds)
 {
   setWindowTitle(tr("Request to Join Your Party"));
-  setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
 
   QPixmap avatar_pixmap;