Remove unnecessary unpolish operation of the style, before polish the new style

src/widget/controlwidgetconnection.cpp

@@ -178,9 +178,6 @@ void ControlWidgetPropertyConnection::slotControlValueChanged(double v) {
 
     m_propertyValue = vParameter;
 
-    // According to http://stackoverflow.com/a/3822243 this is the least
-    // expensive way to restyle just this widget.
-    pWidget->style()->unpolish(pWidget);
     pWidget->style()->polish(pWidget);
 
     // These calls don't always trigger the repaint, so call it explicitly.

src/widget/wcolorpicker.cpp

@@ -234,7 +234,6 @@ void WColorPicker::setColorButtonChecked(const mixxx::RgbColor::optional_t& colo
         pButton->setIcon(QIcon(checked ? ":/images/ic_checkmark.svg" : ""));
     }
     // This is needed to re-apply skin styles (e.g. to show/hide a checkmark icon)
-    pButton->style()->unpolish(pButton);
     pButton->style()->polish(pButton);
 }
 

src/widget/wpushbutton.cpp

@@ -283,12 +283,6 @@ void WPushButton::setPixmapBackground(const PixmapSource& source,
 void WPushButton::restyleAndRepaint() {
     emit displayValueChanged(readDisplayValue());
 
-    // According to http://stackoverflow.com/a/3822243 this is the least
-    // expensive way to restyle just this widget.
-    // Since we expect button connections to not change at high frequency we
-    // don't try to detect whether things have changed for WPushButton, we just
-    // re-render.
-    style()->unpolish(this);
     style()->polish(this);
 
     // These calls don't always trigger the repaint, so call it explicitly.

src/widget/wwidgetgroup.cpp

@@ -236,7 +236,6 @@ void WWidgetGroup::setHighlight(int highlight) {
         return;
     }
     m_highlight = highlight;
-    style()->unpolish(this);
     style()->polish(this);
     update();
     emit highlightChanged(m_highlight);