Fix scaling of PixmapButton in layouts

Fix the scaling of `PixmapButton` when used in layouts. In this case `PixmapButton::sizeHint` is queried which used `devicePixelRatio` to divide the size of the active pixmap. As a result the size is always the same in pixels regardless of the scaling factor of the application. This is fixed by removing the calls.

Example: If the scaling factor is 2 then the pixmap will also report twice the size in pixels and hence request more space in layouts, etc. However, if we divide by the device/pixel ratio then the original size of the image/pixmap will be reported and therefore it will be too small in layouts.

The calls to `devicePixelRatio` have been introduced with pull request LMMS#4950 (via commit c3b4d51) which replaced the old Spectrum Analyzer. The pixmaps of the Spectrum Analyzer still look good with this change.

Fixes LMMS#7052.

src/gui/widgets/PixmapButton.cpp

@@ -131,11 +131,11 @@ QSize PixmapButton::sizeHint() const
 {
 	if( ( model() != nullptr && model()->value() ) || m_pressed )
 	{
-		return m_activePixmap.size() / devicePixelRatio();
+		return m_activePixmap.size();
 	}
 	else 
 	{
-		return m_inactivePixmap.size() / devicePixelRatio();
+		return m_inactivePixmap.size();
 	}
 }