Removal of generic stylesheet rule for dropdown

The generic stylesheet rule (* { border: none; })
was overriding specific styles for
the menu-indicator, causing the dropdown arrow
to appear larger than intended. This rule was
removed to restore default or explicitly set
styles for the arrow, ensuring consistent
visual appearance

Task-number: QTBUG-120604
Pick-to: 6.5
Change-Id: If93de1e1595a2155e9a76644a3c615bd432bf53f
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
(cherry picked from commit ebe9a6ca4bd0df04ae88f926eceda6dabe543748)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

examples/widgets/itemviews/customsortfiltermodel/filterwidget.cpp

@@ -46,7 +46,6 @@ FilterWidget::FilterWidget(QWidget *parent)
     optionsButton->setCursor(Qt::ArrowCursor);
 #endif
     optionsButton->setFocusPolicy(Qt::NoFocus);
-    optionsButton->setStyleSheet("* { border: none; }");
     optionsButton->setIcon(icon);
     optionsButton->setMenu(menu);
     optionsButton->setPopupMode(QToolButton::InstantPopup);