Fix minor compiler warning from Clang

Fixes:
.../qcolorspace_p.h:70:25: warning: explicitly defaulted copy assignment operator is implicitly deleted [-Wdefaulted-function-deleted]
    QColorSpacePrivate &operator=(const QColorSpacePrivate &other) = default;
                        ^
.../qcolorspace_p.h:63:28: note: copy assignment operator of 'QColorSpacePrivate' is implicitly deleted because base class 'QSharedData' has an inaccessible copy assignment operator
class QColorSpacePrivate : public QSharedData
                           ^

Change-Id: I20d453279ec2cb8b9b9d1364762c6e560d6f843d
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/gui/painting/qcolorspace_p.h

@@ -93,7 +93,6 @@ public:
     QColorSpacePrivate(QColorSpace::Gamut gamut, QColorSpace::TransferFunction fun, float gamma);
     QColorSpacePrivate(const QColorSpacePrimaries &primaries, QColorSpace::TransferFunction fun, float gamma);
     QColorSpacePrivate(const QColorSpacePrivate &other) = default;
-    QColorSpacePrivate &operator=(const QColorSpacePrivate &other) = default;
 
     void initialize();
     void setToXyzMatrix();