fix: remove redundant palette setup in RoundScrollArea

1. Removed unnecessary palette initialization in constructor that was
setting window brush to transparent
2. Changed paintEvent to directly use Qt::transparent instead of
palette().window()
3. This simplifies the code while maintaining the same visual effect
of transparency
4. The palette setup was redundant since we're manually painting the
background anyway

fix: 移除RoundScrollArea中多余的调色板设置

1. 移除构造函数中不必要的调色板初始化（将窗口画刷设置为透明）
2. 修改paintEvent直接使用Qt::transparent替代palette().window()
3. 在保持相同透明视觉效果的同时简化了代码
4. 调色板设置是多余的，因为我们已经手动绘制背景

Pms: bug-315535

Author: wjyrich

plugins/dde-dock/util/roundscrollarea.cpp

@@ -16,9 +16,6 @@ RoundScrollArea::RoundScrollArea(QWidget *parent)
     : QScrollArea(parent)
     , m_radius(18)
 {
-    DPalette pa = DPaletteHelper::instance()->palette(this);
-    pa.setBrush(DPalette::Window, Qt::transparent);
-    DPaletteHelper::instance()->setPalette(this, pa);
 }
 
 void RoundScrollArea::setRadius(int radius)
@@ -35,5 +32,5 @@ void RoundScrollArea::paintEvent(QPaintEvent *e)
     QPainterPath path;
     path.addRoundedRect(viewport()->rect(), m_radius, m_radius);
     painter.setClipPath(path);
-    painter.fillPath(path, palette().window());
+    painter.fillPath(path, Qt::transparent);
 }