QColorSpace: remove a redundant declaration

The same function was declared, as friend, a few lines above.

Change-Id: I28368202c68242f2d30d25bd38f2f0e530a60082
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/gui/painting/qcolorspace.h

@@ -132,7 +132,6 @@ private:
 #endif
 };
 
-bool Q_GUI_EXPORT operator==(const QColorSpace &colorSpace1, const QColorSpace &colorSpace2);
 inline bool operator!=(const QColorSpace &colorSpace1, const QColorSpace &colorSpace2)
 {
     return !(colorSpace1 == colorSpace2);