cmake-gui: Fix icon overlay on windows

Since commit 9175a378f5 (QtDialog: Add windows taskbar progress,
2018-11-17, v3.14.0-rc1~330^2) we've added a missing overlay icon.
This results in Windows falling back to a default overlay icon.
Simply drop this line.

Fixes: #19160

Source/QtDialog/CMakeSetupDialog.cxx

@@ -303,7 +303,6 @@ void CMakeSetupDialog::initialize()
 #ifdef QT_WINEXTRAS
   this->TaskbarButton = new QWinTaskbarButton(this);
   this->TaskbarButton->setWindow(this->windowHandle());
-  this->TaskbarButton->setOverlayIcon(QIcon(":/loading.png"));
 #endif
 }